The noun loot was first attested in a 1788 English-Hindi dictionary, with the same definition as today. It wasn't used in the context of actual English until the mid-nineteenth century, but was quickly picked up after that. As Hindi lut, it pretty much meant the same thing, and that comes from the Sanskrit verb lunt, meaning "to rob", so still very similar. Finally, it's thought that lunt derives from the Proto-Indo-European reconstruction reup, meaning "snatch". If you search literary usage of loot over time, you'll see that loot was in use well before 1788; that's because, in certain English dialects, loot has also referred to a type of ladle (this sense has a completely different etymology, coming from Dutch loet) and served as a slang word for lieutenant. The verb form first appeared in 1842.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.