-culum

• (Classical) IPA^(key): /ku.lum/, [kʊɫ̪ʊ̃ˑ]
• (modern Italianate Ecclesiastical) IPA^(key): /ku.lum/, [kulum] (stressed on the antepenult)

From -culus (diminutive suffix).

-culum

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

From (with anaptyxis) Proto-Italic *-klom, from Proto-Indo-European *-tlom, from *-trom. Compare stabulum, which comes from a similar suffix *-dʰlom. Despite the resemblance, ōsculum (which besides is never found in the form **ōsclum) and other diminutive nouns do not contain this suffix.

• -clum, -crum, -ulum

-culum n (genitive -culī); second declension

1. suffix used to form some nouns derived from verbs, particularly nouns representing tools and instruments

The main form of this suffix is -culum. After a stem ending in a velar plosive (spelled c or g), the stem-final consonant merges with the initial consonant of the suffix, causing it to take the alternative form -ulum, as in cingulum. The alternative form -crum, found in words like lavācrum, can occur only when /l/ is present somewhere earlier in the word; it originated from *-klom by long distance dissimilation (compare -ālis and its allomorph -āris). The non-dissimilated form -culum can also be found after /l/ in some words, such as liāculum. All of these variants come from Proto-Indo-European *-tlom.

The suffix -trum originates from the Proto-Indo-European variant form *-trom; it is less common than -culum. The instrument noun suffix is always -trum when it occurs directly after /s/ (as in haustrum); otherwise, the occurrence of -trum appears to be linked to the presence of a liquid /r/ or /l/ somewhere earlier in the word (as in arātrum, tālitrum), but this is not a productive rule.

The form -rum occurs after a stem containing /l/ in the words scalprum and fulcrum (from either *-tlom or *-trom, with simplification after a labial or velar plosive).

The suffix -bulum (dissimilated form -brum) is etymologically related and semantically similar.

Most of these suffixes have variant first-declension feminine forms, such as -cula, -ula, -tra, -bula, -bra (as in pavīcula, dēcipula, mulctra, sūbula, dolābra). A few words appear to show variant second-declension masculine forms, such as culter, scalper.

Second-declension noun (neuter).

From -āculum (by rebracketing of the first-conjugation thematic vowel -ā-):

• Catalan: -all
• French: -ail, -aille
• Italian: -acchio
• Portuguese: -alho
• Spanish: -ajo

• The Proto-Indo-European Instrument Noun Suffix *-tlom and its Variants, Birgit Anette Olsen, 1988.

• Clackson, James, Indo-European Word Formation: Proceedings from the International Conference, 2002
• Philip Baldi, The Foundations of Latin, 2002, pp. 304-305