Why is the ninth month called September?
1540s, from Latin convolutus, past participle of convolvere "to roll together," from com- "together" (see com-) + volvere "to roll" (see volvox).
convolution con·vo·lu·tion (kŏn'və-lōō'shən)n.
A form or part that is folded or coiled.
One of the convex folds of the surface of the brain.