| Word | Definitions | Synonyms |
|---|---|---|
| biconcave | (adjective) concave on both sides | Synonyms: concavo-concave |
| cave | (noun) a geological formation consisting of an underground enclosure with access from the surface of the ground or from the sea | - |
| (verb) explore natural caves | Synonyms: spelunk | |
| (verb) hollow out as if making a cave or opening | Synonyms: undermine | |
| concave | (adjective) curving inward | - |
| planoconcave | (adjective) flat on one side and concave on the other | - |