Entasis

Latin, from Ancient Greek ÎÎ½Ï„Î±ÏƒÎ¹Ï‚ (entasis, "tension, straining"), from ÎµÎ½Ï„ÎµÎ¯Î½Ï‰ (enteino, "to stretch or strain tight").

(plural entases)

(architecture) A slight convex curvature introduced into the shaft of a column for aesthetic reasons, or to compensate for the illusion of concavity.

1859, Journal of the Society of Arts, Volume 7, page 484,It was simply the curve of the entasis, approximating infinitely near to a catenary or to a very flat hyperbola. He could not definitely say whether it was one or the other, but it was nearer to these curves than to the old-fashioned straight line.
1950, William Bell Dinsmoor, The Architecture of Ancient Greece: An Account of Its Historic Development, ISBN 0-8196-0283-3, page 168,The entasis varies in different temples and is not found in some, as, for instance, the temple of Athena Nike and in the east portico of the Erechtheum.
1993, Noel W. Smith, Greek and Interbehavioral Psychology, page 125,Entasis occurred a thousand years earlier in the Sarsen stones at Stonehenge in southern England....Entasis is also present in Egyptian obelisks and in the vertical fins of the radiator grill of the Rolls-Royce automobile.
2005, Lothar Haselberger, 4: Bending the Truth: Curvature and Other Refinements of the Parthenon, Jenifer Neils (editor), The Parthenon: From Antiquity to the Present, page 132,Counter to the increased entases of the pronaos and opisthodomos columns, the adjacent anta pillars and longitudinal cella walls received extraordinarily decreased entases that almost, or even fully, reached rectilinearity.