From Latin 'caverna' (hollow), from 'cavus' (hollow), from PIE *kewH- — same root as 'cave,' 'cavity,' and 'excavate.'
A large cave or underground chamber.
From Old French 'caverne' or directly from Latin 'caverna' (a hollow, a grotto, a cave), derived from 'cavus' (hollow, concave), which traces to PIE *ḱowHo- or *ḱeu- (to swell, vault, be hollow). This root is productive across Indo-European: Greek 'koîlos' (hollow), Welsh 'cau' (hollow, closed), Old Irish 'cúa' (hollow). Latin built several derivatives from 'cavus': 'cavus' itself, 'cavea' (cage, hollow enclosure — source of 'cage'), 'excavare' (to hollow out — source of 'excavate'), and
The PIE root's meaning of 'swelling' connects to hollowness through the image of something swollen outward from a center.