Where does “-thēca” come from?

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

Ancestry of “-thēca”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	θήκη	box, chest; grave, tomb; sword sheath
2	Ancient Greek	τίθημι	I put, place, set; I make, cause to be; I make
3	Proto-Indo-European	dʰeh₁-	to do, put, place