Office Settings & Configuration

Fix Word 365 Cannot Add Word to Custom Dictionary

Maira Mehtab Sep 22, 2026 868 views

Question details

The user is unable to add a specific technical word to the Microsoft Word 365 custom dictionary, as the option appears unavailable or the word continues to be flagged.

Product: Microsoft Word 365
Device & OS: not provided
Scenario: Writing or editing a technical document that uses specialized terminology.
Observed behavior: Microsoft Word 365 refuses to add the word to the custom dictionary, likely because it is already in the built-in spelling lexicon but is being flagged by the grammar checker instead of the spelling checker.

Before you start

Check the color of the squiggly line under the word; a red line indicates a spelling issue, while a double blue line indicates a grammar or contextual issue that cannot be fixed by adding the word to a spelling dictionary.

Solution 1Recommended

Exclude the Specific Text from Proofing

Use this method if the word is being flagged incorrectly by grammar rules and cannot be added to the dictionary.

Sometimes a valid word is already in Word's background lexicon but is flagged because its usage in a sentence triggers a grammar warning (e.g., a noun being interpreted as a verb). In these cases, telling Word to skip proofing for that specific text is the best workaround.

Select the flagged word

Highlight the specific word or phrase in your document that is being incorrectly flagged.

Open Set Proofing Language

Navigate to the 'Review' tab on the top ribbon, click on 'Language' in the Language group, and select 'Set Proofing Language'.

Disable proofing for the selection

In the dialog box that appears, check the box next to 'Do not check spelling or grammar' and click 'OK'.

Proofing Disabled: The red or blue squiggly lines under the selected text will disappear, preventing it from being flagged again in this document.

Solution 2

Ignore the Grammar Suggestion

A quick way to dismiss warnings for words already present in the built-in lexicon.

Solution 3

Disable Proofing for Specific Styles

Ideal for technical documents where a specific formatting style is consistently used for specialized terminology.

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1. Download and Install: Visit the WPS website to download the free installation package and install WPS Office on your device.
2. Open Your Document: Launch WPS Writer and open your existing .docx file directly.
3. Edit Without Disruptions: Enjoy editing your technical documents with highly customizable spell check and grammar tools.

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Frequently Asked Questions

Why is the 'Add to Dictionary' option missing when I right-click a word in Word 365?

If 'Add to Dictionary' is missing, the word is likely already recognized by Word's built-in spelling lexicon, but it is being flagged for a grammatical reason or contextual error instead of a spelling mistake.

How can I tell the difference between a spelling and a grammar error in Word?

Word uses a red squiggly underline to indicate a spelling error (where a word is not found in its dictionaries), and a double blue underline to indicate grammatical errors, formatting inconsistencies, or contextual suggestions.

Where can I manually edit my custom dictionary in Microsoft Word?

You can view and edit your custom dictionary by going to File > Options > Proofing, clicking on 'Custom Dictionaries', selecting your default dictionary (usually CUSTOM.DIC), and clicking 'Edit Word List'.

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