Where does “thēsaurus” come from?

thēsaurus (Latin) comes from Ancient Greek θησαυρός, from Ancient Greek τίθημι, from Proto-Indo-European dʰeh₁- — to do, put, place.

Ancestry of “thēsaurus”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	θησαυρός	treasure; vault, repository, chest
2	Ancient Greek	τίθημι	I put, place, set; I make, cause to be; I make
3	Proto-Indo-European	dʰeh₁-	to do, put, place