LATIN DICTIONARYLexicon Latīnum
suffix

-um

-um
Classical[ˈũː]Ecclesiastical[ˈum]

Meaning

  1. morphemefound in -ōrum
  2. morphemefound in -ārum
  3. morphemeregular ending for 3rd-, 4th- and 5th-conjugation terms
  4. morphemeSometimes found instead of -ōrum, -ārum or -ium

Origins

From Proto-Italic *-om, from Proto-Indo-European *-oHom (genitive plural ending).

Quick answers

What does -um mean in Latin?
-um, a suffix, means “found in -ōrum; found in -ārum; regular ending for 3rd-, 4th- and 5th-conjugation terms”.
How do you pronounce -um?
In classical Latin, [ˈũː]; in ecclesiastical (church) Latin, [ˈum].