means Something valued highly, whether wealth, precious objects, or a person or thing held dear.

from From the Greek 'thesauros' — a storehouse or hoard — which traveled into Latin as 'thesaurus,' then softened through Old French 'tresor' before settling into English. So the same root that gives us the word for a book of synonyms once meant a literal treasure-chest of stored-up riches; a thesaurus is, quite honestly, a hoard of words.