The word treasure as a verb was first used in the late 1300s, but as a noun it was loaned in the middle 1100s from the French word tresor. Orthography remains constant as we move back through Old French to Latin, where we trace it to Latin thesaurus, also meaning "treasure" (and, yes, as I've covered in a previous blog post, this is related to our word thesaurus). That derives from Ancient Greek thesauros, which meant "treasure house" and is related to the verb tithenai, meaning "to put" (which is connected through the idea of storing treasure). Tithenai is thought to be a reduplication of the Proto-Indo-European reconstructed root dhe, meaning "to put" as well, and the word treasure has slowly been decreasing in literary references since the pirate days of yore.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd