diff --git a/components/lib/fieldset/Fieldset.d.ts b/components/lib/fieldset/Fieldset.d.ts
index a61d5bfc4..2c065f47f 100755
--- a/components/lib/fieldset/Fieldset.d.ts
+++ b/components/lib/fieldset/Fieldset.d.ts
@@ -79,17 +79,17 @@ export interface FieldsetPassThroughOptions {
      */
     toggler?: FieldsetPassThroughOptionType;
     /**
-     * Used to pass attributes to the toggler icon's DOM element.
+     * Used to pass attributes to the toggle icon's DOM element.
      */
-    togglerIcon?: FieldsetPassThroughOptionType;
+    toggleIcon?: FieldsetPassThroughOptionType;
     /**
-     * Used to pass attributes to the legend title's DOM element.
+     * Used to pass attributes to the legend label's DOM element.
      */
-    legendTitle?: FieldsetPassThroughOptionType;
+    legendLabel?: FieldsetPassThroughOptionType;
     /**
-     * Used to pass attributes to the toggleable content's DOM element.
+     * Used to pass attributes to the content container's DOM element.
      */
-    toggleableContent?: FieldsetPassThroughOptionType;
+    contentContainer?: FieldsetPassThroughOptionType;
     /**
      * Used to pass attributes to the content's DOM element.
      */
@@ -180,9 +180,26 @@ export interface FieldsetSlots {
      */
     legend: () => VNode[];
     /**
+     * @deprecated since v4.0. Use the 'toggleicon' slot instead.
      * Custom toggler icon template.
+     * @param {Object} scope - toggler icon slot's params.
      */
-    togglericon: () => VNode[];
+    togglericon(scope: {
+        /**
+         * Collapsed state as a boolean
+         */
+        collapsed: boolean;
+    }): VNode[];
+    /**
+     * Custom toggler icon template.
+     * @param {Object} scope - toggler icon slot's params.
+     */
+    toggleicon(scope: {
+        /**
+         * Collapsed state as a boolean
+         */
+        collapsed: boolean;
+    }): VNode[];
 }
 
 /**
diff --git a/components/lib/fieldset/Fieldset.vue b/components/lib/fieldset/Fieldset.vue
index 95fb7c7ec..3db820fc7 100755
--- a/components/lib/fieldset/Fieldset.vue
+++ b/components/lib/fieldset/Fieldset.vue
@@ -2,7 +2,7 @@
     <fieldset :class="cx('root')" v-bind="ptmi('root')">
         <legend :class="cx('legend')" v-bind="ptm('legend')">
             <slot v-if="!toggleable" name="legend">
-                <span :id="id + '_header'" :class="cx('legendtitle')" v-bind="ptm('legendtitle')">{{ legend }}</span>
+                <span :id="id + '_header'" :class="cx('legendLabel')" v-bind="ptm('legendLabel')">{{ legend }}</span>
             </slot>
             <a
                 v-if="toggleable"
@@ -17,16 +17,17 @@
                 @keydown="onKeyDown"
                 v-bind="{ ...toggleButtonProps, ...ptm('toggler') }"
             >
-                <slot name="togglericon" :collapsed="d_collapsed">
-                    <component :is="d_collapsed ? 'PlusIcon' : 'MinusIcon'" :class="cx('togglericon')" v-bind="ptm('togglericon')" />
+                <!--TODO: togglericon deprecated since v4.0-->
+                <slot :name="$slots.togglericon ? 'togglericon' : 'toggleicon'" :collapsed="d_collapsed">
+                    <component :is="d_collapsed ? 'PlusIcon' : 'MinusIcon'" :class="cx('toggleIcon')" v-bind="ptm('toggleIcon')" />
                 </slot>
                 <slot name="legend">
-                    <span :class="cx('legendtitle')" v-bind="ptm('legendtitle')">{{ legend }}</span>
+                    <span :class="cx('legendLabel')" v-bind="ptm('legendLabel')">{{ legend }}</span>
                 </slot>
             </a>
         </legend>
         <transition name="p-toggleable-content" v-bind="ptm('transition')">
-            <div v-show="!d_collapsed" :id="id + '_content'" :class="cx('toggleablecontent')" role="region" :aria-labelledby="id + '_header'" v-bind="ptm('toggleablecontent')">
+            <div v-show="!d_collapsed" :id="id + '_content'" :class="cx('contentContainer')" role="region" :aria-labelledby="id + '_header'" v-bind="ptm('contentContainer')">
                 <div :class="cx('content')" v-bind="ptm('content')">
                     <slot></slot>
                 </div>
diff --git a/components/lib/fieldset/style/FieldsetStyle.js b/components/lib/fieldset/style/FieldsetStyle.js
index b2f7ac33b..52ddb84a5 100644
--- a/components/lib/fieldset/style/FieldsetStyle.js
+++ b/components/lib/fieldset/style/FieldsetStyle.js
@@ -8,9 +8,9 @@ const classes = {
         }
     ],
     legend: 'p-fieldset-legend',
-    legendtitle: 'p-fieldset-legend-label',
-    togglericon: 'p-fieldset-toggle-icon',
-    toggleablecontent: 'p-fieldset-content-container',
+    legendLabel: 'p-fieldset-legend-label',
+    toggleIcon: 'p-fieldset-toggle-icon',
+    contentContainer: 'p-fieldset-content-container',
     content: 'p-fieldset-content'
 };
 
diff --git a/components/lib/panel/Panel.d.ts b/components/lib/panel/Panel.d.ts
index 0382d7464..ba4614dd6 100755
--- a/components/lib/panel/Panel.d.ts
+++ b/components/lib/panel/Panel.d.ts
@@ -94,18 +94,18 @@ export interface PanelPassThroughOptions {
      */
     title?: PanelPassThroughOptionType;
     /**
-     * Used to pass attributes to the icons' DOM element.
+     * Used to pass attributes to the header actions' DOM element.
      */
-    icons?: PanelPassThroughOptionType;
+    headerActions?: PanelPassThroughOptionType;
     /**
-     * Used to pass attributes to the toggler button's DOM element.
+     * Used to pass attributes to the toggle button button's DOM element.
      * @see {@link ButtonPassThroughOptions}
      */
-    toggler?: ButtonPassThroughOptions<PanelSharedPassThroughMethodOptions>;
+    toggleButton?: ButtonPassThroughOptions<PanelSharedPassThroughMethodOptions>;
     /**
-     * Used to pass attributes to the toggleablecontent's DOM element.
+     * Used to pass attributes to the content container's DOM element.
      */
-    toggleableContent?: PanelPassThroughOptionType;
+    contentContainer?: PanelPassThroughOptionType;
     /**
      * Used to pass attributes to the content's DOM element.
      */
@@ -214,6 +214,7 @@ export interface PanelSlots {
      */
     icons(): VNode[];
     /**
+     * @deprecated since v4.0. Use the 'toggleicon' slot instead.
      * Custom toggler icon template of panel.
      * @param {Object} scope - toggler icon slot's params.
      */
@@ -223,6 +224,16 @@ export interface PanelSlots {
          */
         collapsed: boolean;
     }): VNode[];
+    /**
+     * Custom toggler icon template of panel.
+     * @param {Object} scope - toggler icon slot's params.
+     */
+    toggleicon(scope: {
+        /**
+         * Collapsed state as a boolean
+         */
+        collapsed: boolean;
+    }): VNode[];
     /**
      * Custom footer template.
      */
diff --git a/components/lib/panel/Panel.vue b/components/lib/panel/Panel.vue
index d8a69b8ed..e6d6613ee 100755
--- a/components/lib/panel/Panel.vue
+++ b/components/lib/panel/Panel.vue
@@ -4,12 +4,12 @@
             <slot :id="id + '_header'" name="header" :class="cx('title')">
                 <span v-if="header" :id="id + '_header'" :class="cx('title')" v-bind="ptm('title')">{{ header }}</span>
             </slot>
-            <div :class="cx('icons')" v-bind="ptm('icons')">
+            <div :class="cx('headerActions')" v-bind="ptm('headerActions')">
                 <slot name="icons"></slot>
                 <Button
                     v-if="toggleable"
                     :id="id + '_header'"
-                    :class="cx('toggler')"
+                    :class="cx('toggleButton')"
                     :aria-label="buttonAriaLabel"
                     :aria-controls="id + '_content'"
                     :aria-expanded="!d_collapsed"
@@ -17,18 +17,19 @@
                     @click="toggle"
                     @keydown="onKeyDown"
                     v-bind="toggleButtonProps"
-                    :pt="ptm('toggler')"
+                    :pt="ptm('toggleButton')"
                 >
                     <template #icon="slotProps">
-                        <slot name="togglericon" :collapsed="d_collapsed">
-                            <component :is="d_collapsed ? 'PlusIcon' : 'MinusIcon'" :class="slotProps.class" v-bind="ptm('toggler')['icon']" />
+                        <!--TODO: togglericon deprecated since v4.0-->
+                        <slot :name="$slots.togglericon ? 'togglericon' : 'toggleicon'" :collapsed="d_collapsed">
+                            <component :is="d_collapsed ? 'PlusIcon' : 'MinusIcon'" :class="slotProps.class" v-bind="ptm('toggleButton')['icon']" />
                         </slot>
                     </template>
                 </Button>
             </div>
         </div>
         <transition name="p-toggleable-content" v-bind="ptm('transition')">
-            <div v-show="!d_collapsed" :id="id + '_content'" :class="cx('toggleablecontent')" role="region" :aria-labelledby="id + '_header'" v-bind="ptm('toggleablecontent')">
+            <div v-show="!d_collapsed" :id="id + '_content'" :class="cx('contentContainer')" role="region" :aria-labelledby="id + '_header'" v-bind="ptm('contentContainer')">
                 <div :class="cx('content')" v-bind="ptm('content')">
                     <slot></slot>
                 </div>
diff --git a/components/lib/panel/style/PanelStyle.js b/components/lib/panel/style/PanelStyle.js
index 06c847d9a..430c4b82a 100644
--- a/components/lib/panel/style/PanelStyle.js
+++ b/components/lib/panel/style/PanelStyle.js
@@ -9,9 +9,9 @@ const classes = {
     ],
     header: 'p-panel-header',
     title: 'p-panel-title',
-    icons: 'p-panel-header-actions',
-    toggler: 'p-panel-toggle-button',
-    toggleablecontent: 'p-panel-content-container',
+    headerActions: 'p-panel-header-actions',
+    toggleButton: 'p-panel-toggle-button',
+    contentContainer: 'p-panel-content-container',
     content: 'p-panel-content',
     footer: 'p-panel-footer'
 };