-ulum

A phonologically conditioned alteration (allomorph) of Latin -culum, from Proto-Indo-European *-tlom, generated by a rule deleting the suffix-initial stop in positions after stops.

• (Classical Latin) IPA^(key): /u.lum/, [ʊɫ̪ʊ̃ˑ]
• (modern Italianate Ecclesiastical) IPA^(key): /u.lum/, [ulum] (stressed on the antepenult)

-ulum n (genitive -ulī); second declension

1. Used to form a noun of instrument or means from a verb.

   ‎amicio + ‎-ulum → ‎amiculum

   ‎specio + ‎-ulum → ‎speculum < *spek-klo- < *spek-tlo-

   ‎cingo + ‎-ulum → ‎cingulum

Second-declension noun (neuter).

Inflected from -ulus.

-ulum

1. inflection of -ulus:
   1. nominative/accusative/vocative neuter singular
   2. accusative masculine singular

• Clackson, James, Indo-European Word Formation: Proceedings from the International Conference, 2002.