Latin word rotundus comes from Latin rotare, Latin -undus

Detailed word origin of rotundus

Dictionary entry	Language	Definition
rotare	Latin (lat)
-undus	Latin (lat)	Derives adjective nouns from verbs, similar to present participles, but without the present time restriction.
rotundus	Latin (lat)	(figuratively) rounded, perfect. (figuratively, of speech) polished, elegant. (substantive) A sphere. Round, circular. Spherical, rotund.