Some interesting words I’ve run across recently:
1) I was watching Jia Zhangke’s movie Ash Is Purest White, about a couple involved in the (pretty petty) underworld milieu of Datong, and was intrigued to note that the subtitles didn’t translate the word jianghu (e.g., “You’re no longer in the jianghu”). I paused the movie to look it up and discovered it’s such a complex concept the choice to leave it in Chinese made sense:
Jianghu (江湖; jiānghú; gong¹wu⁴; ‘rivers and lakes’) is a Chinese term that generally refers to the social environment in which many Chinese wuxia, xianxia, and gong’an stories are set. The term is used flexibly, and can be used to describe a fictionalized version of rural historical China (usually using loose influences from across the ~1000 BC–280 AD period); a setting of feuding martial arts clans and the people of that community; a secret and possibly criminal underworld; a general sense of the “mythic world” where fantastical stories happen; or some combination thereof.
See the Wikipedia article for the derivation from Zhuangzi and various interpretations and uses. The Chinese title of the movie is 江湖儿女 ‘Sons and Daughters of (the) Jianghu,’ which certainly gives the prospective viewer more of a heads-up than the mysterious English one.
2) I forget where I ran across the French word bistouri ‘scalpel,’ but it’s got an interesting history; Wiktionary:
Borrowed from Italian pistorese or pistorino (“from Pistoia”, see Latin Pistōrium); the city of Pistoia was once famous for the manufacturing of blades.
It was borrowed into English as bistoury /ˈbɪstəɹi/, of which the OED (entry from 1887) says “Surgery. A scalpel; made in three forms, the straight, the curved, and the probe-pointed (which is also curved).” The etymology, after deriving it from French, adds “Said in some books to be < Pistorium, now Pistoja; but this is merely a conjecture from the similarity of the words.” I hope Xerîb will have something to say.
3) In Alaina Demopoulos’s Grauniad thumbsucker “Is it OK to read Infinite Jest in public? Why the internet hates ‘performative reading’” (archived), I was baffled by the first noun in “And maybe there’s still some steeze that comes from flexing an ‘important’ book.” Turns out steez(e) (which has not made it into the OED) means ‘a person’s distinctive and attractive or impressive style of dress or way of doing things’; Green says [SE style + -ɪᴢ- infix] and takes it back to 1990 (Run-DMC ‘Bob Your Head’ 
Weave with ease and please the steez with G’s). The ever-hip NY Times was onto it by 2007 (Anne Goodwin Sides, “Snowbound Neverland in Colorado“: “‘Right now I’m learning to pop off of jumps with steeze’ — style”), but it had somehow eluded me until now.