1. Anandamide, the endogenous cannabanoid neurotransmitter; name comes from “the Sanskrit word ananda, which means ‘joy, bliss, delight.'” (I guess Vishy Anand, the chess player, gets his family name from this word too!)
2. Coprolalia, the word for clinical profanity. Coprolalia comes from the Greek κόπρος (kopros) meaning “feces” and λαλιά (lalia) from lalein, “to talk”. Literally means to talk shit.
3. Orthodoxy means “true/correct belief” (a normative claim, really, which makes it really interesting that sects of some religions are described as Orthodox). Relatedly: Orthogonal, meaning of right angles, comes from the same “ortho” root meaning correct. That means that “right” angles more generally means “true” or “correct” angles!

I’m sure there are dozens of interesting etymologies like these. Semi-related: the word velleity is really neat. Also this rebuke of the word “problematic.”