-culum

Etymology 1
From.

Etymology 2
From (with anaptyxis), from , from. Compare, which comes from a similar suffix. Despite the resemblance, (which besides is never found in the form **ōsclum) and other diminutive nouns do not contain this suffix.

Usage notes
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, as in. The alternative form, found in words like , can occur only when /l/ is present somewhere earlier in the word; it originated from *-klom by long distance dissimilation (compare and its allomorph ). The non-dissimilated form -culum can also be found after /l/ in some words, such as. All of these variants come from Proto-Indo-European *-tlom.

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

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

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

Most of these suffixes have variant first-declension feminine forms, such as, , , , (as in , , , , ). Variant second-declension masculine forms are less common, but are attested in a few nouns, such as, (a variant of ), and the plural.

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