- to explore caves, especially as a hobby.
Origin of spelunk
back formation from spelunker, spelunking
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
"cave, cavern," c.1300, from Old French spelonque or directly from Latin spelunca "a cave, cavern, grotto," from Greek spelynx (genitive spelyngos). An adjective, speluncar "of a cave" is recorded from 1855.
Online Etymology Dictionary, © 2010 Douglas Harper