octodecim

• Symbol: XVIII

From octō (“eight”) + decem (“ten”).

• (Classical) IPA^(key): /okˈtoː.de.kim/, [ɔkˈtoː.dɛ.kĩ]
• (Ecclesiastical) IPA^(key): /okˈto.de.t͡ʃim/, [okˈtoː.de.t͡ʃim]

octōdecim (indeclinable)

1. (rare) eighteen; 18
   • 1543, Petrus Comestor, Historia Scholastica, III Kings, "De porticu"

     Quarum talis erat compositio: Stylus, vel stipes columnae octodecim habebat cubitos altitudinis

   • 1687, Isaac Newton, Philosophiae Naturalis Principia Mathematica, "Axiomata, sive Leges Motus"

     Si corpus Alucretur partes novem vel decem vel undecim vel duodecim, adeoque progrediatur post concursum cum partibus quindecim vel sexdecim vel septendecim vel octodecim.

This form is rare, and is found primarily in bookish post-Classical Latin. The usual word for eighteen in Classical Latin is duodēvīgintī.

• duodēvīgintī

• Appendix:Latin cardinal numbers

• octodecim in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• octodecim in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
• octodecim in Gaffiot, Félix (1934) Dictionnaire Illustré Latin-Français, Hachette