diff --git a/dev/translator-vm.js b/dev/translator-vm.js
index 8397b65e..f68b25db 100644
--- a/dev/translator-vm.js
+++ b/dev/translator-vm.js
@@ -170,6 +170,12 @@ class TranslatorVM extends DatabaseVM {
             enabledDictionaryMap = new Map(enabledDictionaryMap);
             options.enabledDictionaryMap = enabledDictionaryMap;
         }
+        const {excludeDictionaryDefinitions} = options;
+        options.excludeDictionaryDefinitions = (
+            Array.isArray(excludeDictionaryDefinitions) ?
+            new Set(excludeDictionaryDefinitions) :
+            null
+        );
 
         return options;
     }
diff --git a/ext/js/background/backend.js b/ext/js/background/backend.js
index 42b03c59..33650319 100644
--- a/ext/js/background/backend.js
+++ b/ext/js/background/backend.js
@@ -411,7 +411,7 @@ class Backend {
     async _onApiTermsFind({text, details, optionsContext}) {
         const options = this._getProfileOptions(optionsContext);
         const {general: {resultOutputMode: mode, maxResults}} = options;
-        const findTermsOptions = this._getTranslatorFindTermsOptions(details, options);
+        const findTermsOptions = this._getTranslatorFindTermsOptions(mode, details, options);
         const {dictionaryEntries, originalTextLength} = await this._translator.findTerms(mode, text, findTermsOptions);
         dictionaryEntries.splice(maxResults);
         return {dictionaryEntries, originalTextLength};
@@ -1044,14 +1044,15 @@ class Backend {
     async _textParseScanning(text, options) {
         const jp = this._japaneseUtil;
         const {scanning: {length: scanningLength}, parsing: {readingMode}} = options;
-        const findTermsOptions = this._getTranslatorFindTermsOptions({wildcard: null}, options);
+        const mode = 'simple';
+        const findTermsOptions = this._getTranslatorFindTermsOptions(mode, {wildcard: null}, options);
         const results = [];
         let previousUngroupedSegment = null;
         let i = 0;
         const ii = text.length;
         while (i < ii) {
             const {dictionaryEntries, originalTextLength} = await this._translator.findTerms(
-                'simple',
+                mode,
                 text.substring(i, i + scanningLength),
                 findTermsOptions
             );
@@ -1869,7 +1870,7 @@ class Backend {
         this._applyOptions(source);
     }
 
-    _getTranslatorFindTermsOptions(details, options) {
+    _getTranslatorFindTermsOptions(mode, details, options) {
         const {wildcard} = details;
         const enabledDictionaryMap = this._getTranslatorEnabledDictionaryMap(options);
         const {
@@ -1886,6 +1887,16 @@ class Backend {
             }
         } = options;
         const textReplacements = this._getTranslatorTextReplacements(textReplacementsOptions);
+        let excludeDictionaryDefinitions = null;
+        if (mode === 'merge' && !enabledDictionaryMap.has(mainDictionary)) {
+            enabledDictionaryMap.set(mainDictionary, {
+                index: enabledDictionaryMap.size,
+                priority: 0,
+                allowSecondarySearches: false
+            });
+            excludeDictionaryDefinitions = new Set();
+            excludeDictionaryDefinitions.add(mainDictionary);
+        }
         return {
             wildcard,
             mainDictionary,
@@ -1897,7 +1908,8 @@ class Backend {
             convertKatakanaToHiragana,
             collapseEmphaticSequences,
             textReplacements,
-            enabledDictionaryMap
+            enabledDictionaryMap,
+            excludeDictionaryDefinitions
         };
     }
 
diff --git a/ext/js/language/translator.js b/ext/js/language/translator.js
index d416d405..bf2c7322 100644
--- a/ext/js/language/translator.js
+++ b/ext/js/language/translator.js
@@ -85,13 +85,14 @@ class Translator {
      *         priority: (number),
      *         allowSecondarySearches: (boolean)
      *       }
-     *     ])
+     *     ]),
+     *     excludeDictionaryDefinitions: (Set of (string) or null)
      *   }
      * ```
      * @returns An object of the structure `{dictionaryEntries, originalTextLength}`.
      */
     async findTerms(mode, text, options) {
-        const {enabledDictionaryMap} = options;
+        const {enabledDictionaryMap, excludeDictionaryDefinitions} = options;
         let {dictionaryEntries, originalTextLength} = await this._findTermsInternal(text, enabledDictionaryMap, options);
 
         switch (mode) {
@@ -103,6 +104,10 @@ class Translator {
                 break;
         }
 
+        if (excludeDictionaryDefinitions !== null) {
+            this._removeExcludedDefinitions(dictionaryEntries, excludeDictionaryDefinitions);
+        }
+
         if (dictionaryEntries.length > 1) {
             this._sortTermDictionaryEntries(dictionaryEntries);
         }
@@ -492,6 +497,101 @@ class Translator {
         return newDictionaryEntries;
     }
 
+    _removeExcludedDefinitions(dictionaryEntries, excludeDictionaryDefinitions) {
+        for (let i = dictionaryEntries.length - 1; i >= 0; --i) {
+            const dictionaryEntry = dictionaryEntries[i];
+            const {definitions, pronunciations, frequencies, headwords} = dictionaryEntry;
+            const definitionsChanged = this._removeArrayItemsWithDictionary(definitions, excludeDictionaryDefinitions);
+            this._removeArrayItemsWithDictionary(pronunciations, excludeDictionaryDefinitions);
+            this._removeArrayItemsWithDictionary(frequencies, excludeDictionaryDefinitions);
+            this._removeTagGroupsWithDictionary(definitions, excludeDictionaryDefinitions);
+            this._removeTagGroupsWithDictionary(headwords, excludeDictionaryDefinitions);
+
+            if (!definitionsChanged) { continue; }
+
+            if (definitions.length === 0) {
+                dictionaryEntries.splice(i, 1);
+            } else {
+                this._removeUnusedHeadwords(dictionaryEntry);
+            }
+        }
+    }
+
+    _removeUnusedHeadwords(dictionaryEntry) {
+        const {definitions, pronunciations, frequencies, headwords} = dictionaryEntry;
+        const removeHeadwordIndices = new Set();
+        for (let i = 0, ii = headwords.length; i < ii; ++i) {
+            removeHeadwordIndices.add(i);
+        }
+        for (const {headwordIndices} of definitions) {
+            for (const headwordIndex of headwordIndices) {
+                removeHeadwordIndices.delete(headwordIndex);
+            }
+        }
+
+        if (removeHeadwordIndices.size === 0) { return; }
+
+        const indexRemap = new Map();
+        let oldIndex = 0;
+        for (let i = 0, ii = headwords.length; i < ii; ++i) {
+            if (removeHeadwordIndices.has(i)) {
+                headwords.splice(i, 1);
+                --i;
+                --ii;
+            } else {
+                indexRemap.set(oldIndex, indexRemap.size);
+            }
+            ++oldIndex;
+        }
+
+        this._updateDefinitionHeadwordIndices(definitions, indexRemap);
+        this._updateArrayItemsHeadwordIndex(pronunciations, indexRemap);
+        this._updateArrayItemsHeadwordIndex(frequencies, indexRemap);
+    }
+
+    _updateDefinitionHeadwordIndices(definitions, indexRemap) {
+        for (const {headwordIndices} of definitions) {
+            for (let i = headwordIndices.length - 1; i >= 0; --i) {
+                const newHeadwordIndex = indexRemap.get(headwordIndices[i]);
+                if (typeof newHeadwordIndex === 'undefined') {
+                    headwordIndices.splice(i, 1);
+                } else {
+                    headwordIndices[i] = newHeadwordIndex;
+                }
+            }
+        }
+    }
+
+    _updateArrayItemsHeadwordIndex(array, indexRemap) {
+        for (let i = array.length - 1; i >= 0; --i) {
+            const item = array[i];
+            const {headwordIndex} = item;
+            const newHeadwordIndex = indexRemap.get(headwordIndex);
+            if (typeof newHeadwordIndex === 'undefined') {
+                array.splice(i, 1);
+            } else {
+                item.headwordIndex = newHeadwordIndex;
+            }
+        }
+    }
+
+    _removeArrayItemsWithDictionary(array, excludeDictionaryDefinitions) {
+        let changed = false;
+        for (let j = array.length - 1; j >= 0; --j) {
+            const {dictionary} = array[j];
+            if (!excludeDictionaryDefinitions.has(dictionary)) { continue; }
+            array.splice(j, 1);
+            changed = true;
+        }
+        return changed;
+    }
+
+    _removeTagGroupsWithDictionary(array, excludeDictionaryDefinitions) {
+        for (const {tags} of array) {
+            this._removeArrayItemsWithDictionary(tags, excludeDictionaryDefinitions);
+        }
+    }
+
     // Tags
 
     _getTermTagTargets(dictionaryEntries) {