Entasis
WordNet
noun
(1) A slight convexity in the shaft of a column; compensates for the illusion of concavity that viewers experience when the sides are perfectly straight
WiktionaryText
Etymology
Modern Latin, from Ancient Greek έντασις (entasis) "tension, straining", from εντείνω (enteino) "to stretch or strain tight".
Noun
entasis
- a slight curvature introduced into the shaft of a column to create the impression of concavity; a deliberate bowing