undec(a)-
Eleven.
Latin undecim, eleven.
An undecagon (Greek ‑gōnos, -angled) is a plane figure with eleven straight sides and angles; undecane (see ‑ane1) is a hydrocarbon of chemical formula C11H24; the related fatty acid is undecanoic acid, one form of which, produced from castor oil and used in perfumery, is commonly called undecylenic acid.
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