dodecagon
Concise Oxford English Dictionary © 2008 Oxford University Press:
dodecagon /dəʊˈdɛkəg(ə)n/
▶noun a plane figure with twelve straight sides and angles.
– origin C17: from Gk dōdekagōnon, neut. (used as a noun) of dōdekagōnos ‘twelve-angled’.
'dodecagon' also found in these Oxford entries:

