What is the Latin word for eighteen?

The usual Latin words for “eighteen” are duodēvīgintī, duodēvīcēnus. The right choice depends on the sense; see the distinctions below.

English → Latin

“eighteen” in Latin

duodēvīgintīeighteen; 18 duodēvīcēnuseighteen each

Riddle & Arnold A Copious and Critical English–Latin Lexicon, 1864

eighteen

duodeviginti; (less commonly) decem et octo: duodeviceni (distributively): boys of eighteen years old, pueri duodevicenum annorum: eighteen letters, duodevicenae litterae: but, eighteen letters (of the alphabet), duodeviginti litterae: eighteen months, sex mensium et anni spatium: eighteen years old, duodeviginti annorum; duodeviginti annos natus: eighteen times, *duodevicies: eighteen times as large, *duodeviginti partibus major.

Quick answer

What is the Latin word for eighteen?: The usual Latin words for “eighteen” are duodēvīgintī, duodēvīcēnus. The right choice depends on the sense; see the distinctions below.

Entry from J. E. Riddle & T. K. Arnold, A Copious and Critical English–Latin Lexicon (rev. C. Anthon, New York: Harper, 1864), digitised by Fergus J. P. Walsh, CC BY-SA 4.0; Latin markup adapted by latindictionary.co.