How to Set Word Custom Dictionary for Domain-Specific Compound Words

When you type domain-specific compound words like “machine-learning algorithm” or “API-first design,” Word often flags them as spelling errors. The default dictionary does not include technical terms, brand names, or hyphenated compounds common in industries such as law, medicine, engineering, or software development. This article explains how to create and manage a custom dictionary in Word so that these specialized terms are recognized and never underlined as mistakes.

What a Custom Dictionary Does and Why You Need One

Word uses the default dictionary to check spelling against standard English words. Domain-specific compound words—such as “cloud-native,” “data-driven,” or “user-centric”—are often hyphenated or concatenated in ways the default dictionary does not accept. When Word encounters these terms, it underlines them in red and suggests corrections that break the intended meaning.

A custom dictionary is a plain text file with a .dic extension where you store words that Word should treat as correctly spelled. You can create multiple custom dictionaries, each tailored to a specific field or project. For example, a medical writer might have a dictionary with terms like “patient-centered” and “evidence-based,” while a software engineer might add “back-end,” “front-end,” and “API-first.”

How Word Handles Compound Words

Word’s spell checker processes each word individually. Hyphenated compounds are split at the hyphen, and each part is checked separately. If either part is missing from the dictionary, the entire compound is flagged. By adding the full compound to a custom dictionary, you tell Word to accept the hyphenated form as a single valid entry.

Prerequisites

Before setting up a custom dictionary, ensure you have a list of the domain-specific compound words you want to add. You can type them as you encounter them in your documents or compile them from a glossary. No special permissions are needed—any user can create and manage custom dictionaries in Word for Microsoft 365, Word 2021, Word 2019, and earlier versions.

Steps to Create and Edit a Custom Dictionary for Domain-Specific Compound Words

1. Open the Custom Dictionaries dialog
   In Word, go to File > Options > Proofing. Under the “When correcting spelling in Microsoft Office programs” section, click the Custom Dictionaries button. This opens the Custom Dictionaries dialog where all available dictionaries are listed.
2. Create a new custom dictionary
   In the Custom Dictionaries dialog, click New. A file save dialog appears. Name your dictionary with a descriptive title, such as “MedicalTerms.dic” or “SoftwareTerms.dic”. Choose a location you can easily find later—the default folder is usually C:\Users\[YourName]\AppData\Roaming\Microsoft\UProof. Click Save to create the empty dictionary file.
3. Select the new dictionary as the active one
   Back in the Custom Dictionaries dialog, ensure the checkbox next to your new dictionary is checked. If you have multiple dictionaries, only checked ones are used during spell check. You can also change the default dictionary by selecting it and clicking Change Default.
4. Add compound words to the dictionary
   With your new dictionary selected, click Edit Word List. A small window opens where you can type each compound word. For example, type data-driven and click Add. Repeat for every term you need: machine-learning, state-of-the-art, high-quality. When finished, click OK to close the window.
5. Apply the dictionary to your document
   Click OK in the Custom Dictionaries dialog, then click OK in the Word Options dialog. Word now uses the custom dictionary during spell check. Type one of the added compound words in your document—the red underline should disappear.

Common Mistakes, Limitations, and Things to Avoid

Adding only one part of a compound word

If you add only “data” or only “driven” to the custom dictionary, Word will still flag “data-driven” because the hyphenated compound is not recognized as a whole. Always add the complete compound exactly as you want it to appear in your documents, including hyphens or spaces.

Using the wrong dictionary file

Word ships with a default custom dictionary named “Custom.dic”. If you add your domain terms to this file, they will be applied to all documents. For project-specific terms, create a separate dictionary so you can disable it when working on other types of content.

Spell check not using the custom dictionary

If the red underlines persist after adding terms, open the Custom Dictionaries dialog and verify that your dictionary is checked. Also confirm that the “Suggest from main dictionary only” option is unchecked in the Proofing settings. This option, when enabled, ignores custom dictionaries entirely.

Compound words with multiple hyphens

Words like “up-to-date” or “mother-in-law” contain more than one hyphen. Word handles these by checking each segment. Add the full hyphenated string to your custom dictionary exactly as you type it. If you add “up-to-date,” Word will accept it without flagging any part.

Sharing custom dictionaries across devices

Custom dictionaries are stored locally on your computer. If you work on multiple devices, you need to copy the .dic file to the same folder on each machine. You can also store the file in a cloud-synced folder like OneDrive, but ensure Word can access the full path.

Custom Dictionary Methods: Manual Entry vs Import From a Text File

Item	Manual Entry via Edit Word List	Import From a Text File
Description	Type each compound word one by one in the Edit Word List dialog	Create a .txt file with one word per line, then rename it to .dic and copy it to the UProof folder
Best for	Adding a small number of terms (fewer than 50)	Adding hundreds of terms or migrating a dictionary from another system
Steps required	Open dialog, type word, click Add, repeat	Prepare text file, rename extension, place in UProof folder, then add via Custom Dictionaries dialog
Risk of errors	Low; each word is added individually	Medium; ensure the text file has no extra spaces or blank lines

To import from a text file, open Notepad and type one compound word per line, for example:

data-driven
machine-learning
state-of-the-art

Save the file with a .dic extension, such as MyTerms.dic. Copy it to the UProof folder (typically C:\Users\[YourName]\AppData\Roaming\Microsoft\UProof). Then in Word, open the Custom Dictionaries dialog, click Add, browse to the .dic file, and select it. The imported words will appear in the Edit Word List.

You can now manage domain-specific compound words in Word without seeing distracting red underlines. Create separate dictionaries for different projects, switch between them as needed, and import large term lists quickly using a text file. For advanced control, consider using the ExcludeDictionary setting to block certain words from being accepted, though this is rarely needed for compound terms.