C / convexĭo
noun

convexĭo

gen. convexōnis · gender feminine · decl. 3rd
a vaulting, convexity; concavity
a vaulting, convexity, also concavity (post-class.; cf. convexitas): mundi, Gell. 14, 1, 8: rotunditatis solidae, Arn. 4, 129.