LATIN DICTIONARYLexicon Latīnum
adverb

decimum

decimum (not comparable)
Classical[ˈdɛ.kɪ.mũː]Ecclesiastical[ˈdɛː.t͡ʃi.mum]

Meaning

  1. not comparablefor the tenth time

Charlton Lewis's shorter dictionary for students: the same scholarship in plain, modern definitions.

decimum adv.
decimus, for the tenth time , L.

Origins

Adverbial accusative of decimus (“tenth”).

Quick answers

What does decimum mean in Latin?
decimum, a adverb, means “for the tenth time”.
How do you pronounce decimum?
In classical Latin, [ˈdɛ.kɪ.mũː]; in ecclesiastical (church) Latin, [ˈdɛː.t͡ʃi.mum].