spelunk
v. US //spəˈɫəŋk// spelunk
From Middle English spelunke, from Old French spelonque and/or Latin spelunca, from Ancient Greek σπῆλυγξ (spêlunx, “cave”), related to σπέος (spéos). Cognates include Middle Dutch spelunke, spelonke, German Spelunke.
U.S., 1940s. Back-formation from spelunker.