Entasis \En"ta*sis\, n. [NL., from Gr. ? a stretching; fr. ?; ? in + ? to extend.] 1. (Arch.) A slight convex swelling of the shaft of a column. 2. (Med.) Same as {Entasia}.
entasis n : a slight convexity in the shaft of a column; compensates for the illusion of concavity that viewers experience when the sides are perfectly straight [also: {entases} (pl)]