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spelunk (n.)[spelunk 词源字典]: "a cave, cavern, a vault," c. 1300, from Old French spelonque (13c.) or directly from Latin spelunca "a cave, cavern, grotto," from Greek spelynx (accusative spelynga, genitive spelyngos) "a cave, cavern," from spelos "a cave." An adjective, speluncar "of a cave" is recorded from 1855.[spelunk etymology, spelunk origin, 英语词源]
spelunking: "The exploration of caves, especially as a hobby", 1940s: from obsolete spelunk 'cave' (from Latin spelunca) + -ing¹.