the.com/roundel

A circle that means serious business, usually painted on a warplane.

means A small flat circular shape or design, often used as an identifying badge or decorative motif.

from From French 'rondelle,' a little round thing, itself from 'rond' meaning round — ultimately tracing back to Latin 'rotundus.' The word drifted into English in the medieval period and settled into a handy label for anything disc-shaped: a decorative panel, a heraldic circle, a slice of meat, or eventually the national-insignia circle painted on military aircraft to answer the urgent question 'friend or foe?'

origin
heraldry term for a circular charge on a shield
military use
RAF adopted it in 1915 to avoid friendly fire
design logic
concentric colors make instant nation recognition possible
beyond planes
also names round stained glass windows and coins
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