Geom. [Irreg. f. L. undec-im eleven, after decagon (cf. HENDECAGON). So Sp. and Pg. undecágono, F. ondécagone.] A plane figure having eleven sides and angles.
1728. Chambers, Cycl., Undecagon, is a regular Polygon of eleven Sides.
1798. Hutton, Course Math. (1806), I. 271.
1879. Cassell’s Techn. Educ., I. 251.
