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.

6. baby Infant Child Toddler Kid Tot Young one

7. Verb

8. The happy baby walked eagerly around the room.

9. walk Stroll Amble Saunter Step Toddle Meander

10. Adjective

11. The happy baby walked eagerly around the room.

12. happy Merry Gleeful Delighted Cheerful Genial Jolly Jovial

13. Adverb

14. The happy baby walked eagerly around the room.

15. eager Excited Avid Enthusiastic Tireless Exuberant Impulsive

16. The cheerful toddler sauntered exuberantly around the room.