A thesaurus is a book that lists words and their synonyms to help find alternative words. It can be used to replace nouns like "baby" with "infant" or "child", verbs like "walked" with "strolled" or "ambled", adjectives like "happy" with "merry" or "gleeful", and adverbs like "eagerly" with "excitedly" or "avidly". The document provides an example of using a thesaurus to replace words in the sentence "The happy baby walked eagerly around the room" with synonyms.

1. Using a Thesaurus

2. A thesaurus is a book of words and their synonyms.

3. You would use a thesaurus when you want to find a new word to replace a word that you already know.

4. Noun

5. The happy baby walked eagerly around the room.

7. Verb

8. The happy baby walked eagerly around the room.

10. Adjective

11. The happy baby walked eagerly around the room.

13. Adverb

14. The happy baby walked eagerly around the room.

16. The cheerful toddler sauntered exuberantly around the room.