The correct answer is Thesaurus.The Thesaurus is a software tool that is used in the Microsoft Word document to look up (find) synonyms (words with the same meaning) and antonyms (words with the opposite meaning) for the selected word.Generally, the Thesaurus is used in the Word documents when we write an email, letter, project report, or research papers.Additional InformationDictionary: A custom dictionary contains words that are not in the main Office dictionary. You can either create a new dictionary or modify the main dictionary. Custom dictionaries created in Word are shared with the other Office programs. This document contains instructions for creating and editing a custom dictionary using Word.Spell check : In Microsoft Word documents, Words spell check function is set to automatically check our spelling while we type. Errors in our document will have color-coded underlines reflecting your choices, like red for spelling errors, green for grammar errors, and blue for contextual spelling errors.