pendecagon
/pɛnˈdɛkəɡ(ə)n/ /pɛnˈdɛkəɡɒn/Geometry rare
noun
A plane figure having fifteen straight sides and fifteen angles; a quindecagon.
Origin
Late 17th century; earliest use found in William Alingham (fl. 1694–1710). Apparently irregularly from pen- (in ancient Greek πέντε five: see penta-) + decagon. Compare post-classical Latin pentedecagonum, Hellenistic Greek πεντεκαιδεκάγωνον.