from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A slight convexity or swelling, as in the shaft of a column, intended to compensate for the illusion of concavity resulting from straight sides.
The ancient Greeks used a technique known as entasis which incorporates a slight convexity in the columns of the Parthenon to compensate for the illusion of concavity created by parallel lines.
Beard is rather dismissive of their optical sophistication, shown in the curvature of the stylobate and in the entasis of the columns — the slight outward swelling of a column designed to counter the optical illusion of concavity, were the columns' sides to be perfectly straight.
The entasis of columns and curvature of what would ordinarily be straight lines is familiar to all students of architecture.
Peyton had opposed a laughing refusal, enforced by the presence of two fellow-architects, young men with lingering traces of the Beaux Arts in their costume and vocabulary, who stood about in Gavarni attitudes and dazzled the ladies by allusions to fenestration and entasis.
The word 'entasis' comes from a Greek word meaning 'to stretch tight'.