From The Collaborative International Dictionary of English v.0.48:
Roundel \Roun"del\, n. [OF. rondel a roundelay, F. rondel,
rondeau, a dim. fr. rond; for sense 2, cf. F. rondelle a
round, a round shield. See Round, a., and cf. Rondel,
Rondelay.]
1. (Mus.) A rondelay. "Sung all the roundel lustily."
--Chaucer.
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Come, now a roundel and a fairy song. --Shak.
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2. Anything having a round form; a round figure; a circle.
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The Spaniards, casting themselves into roundels, . .
. made a flying march to Calais. --Bacon.
[1913 Webster] Specifically:
(a) A small circular shield, sometimes not more than a
foot in diameter, used by soldiers in the fourteenth
and fifteenth centuries.
(b) (Her.) A circular spot; a sharge in the form of a
small circle.
(c) (Fort.) A bastion of a circular form.
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