The word 'spelunker' is a modern American English formation from the mid-20th century. It derives from the verb 'to spelunk,' which itself was a back-formation from the archaic noun 'spelunk,' meaning cave, borrowed from the Latin 'spelunca.' This Latin term has a deeper ancestry in Ancient Greek, where 'spēlaion' (σπήλαιον) also meant a cave or grotto. The suffix '-er,' a common agentive ending in English, is appended to specify a person who engages in the activity. Thus, the literal construction "cave-person" accurately reflects the modern hobbyist meaning, distinguishing it from the more scientific 'speleologist.'

Structure: spelunk (cave) + er (person who) - spelunk: From Latin 'spelunca' (cave, cavern), via the English verb 'to spelunk' (to explore caves). - er: An English agent noun suffix of Germanic origin, denoting a person associated with an action or thing.