octōdĕcim, card. num. adj. [octo-decem],
eighteen (mostly post-class, for duodeviginti): tetrachma Attica centum octodecim milia, Liv. 39, 5, 14: cohortes, Front. Strat. 2, 5, 37; Eutr. 1, 1.
octōdecim or XVIII num. octo+decem, eighteen , L ...
An Elementary Latin Dictionary