-culus

Etymology
of diminutive suffix on nouns ending in, used freely.

Usage notes
The ending -culus occurs originally and frequently in diminutives formed from third declension nouns with stems ending in /n/ or /s/. It is used also to form diminutives of other third declension nouns (particularly i-stems and r-stems, sometimes others), and of fourth and fifth declension nouns. In the form -iculus, it is sometimes used instead of to form diminutives of other consonant stem nouns or of first or second declension nouns. As with other Latin diminutive suffixes, the gender of the diminutive regularly matches the gender of the base noun.

The unextended form -culus, -cula, -culum cannot directly follow a consonant other than /l/, /n/, /r/, or /s/. The suffix may occur after other consonants with an intervening vowel: The stem that the diminutive is built on is sometimes different from the stem found in the genitive singular of the base:
 * It is often preceded by the short vowel /i/ (-icul-). This occurs in diminutives of some third declension nouns and in diminutives of fourth declension nouns (where /i/ replaces the stem-final /u/ of the base noun, as in, and  from , , ). Etymologically, this /i/ is derived in some cases from the final vowel of the stem (affected when possible by vowel reduction): many words that form diminutives in -icul- were originally i-stem forms (whether of the "pure" parisyllabic or neuter types, or the "mixed" type that resulted from contraction in the nominative singular). However, -icul- can also be found in diminutives of third-declension words that are etymologically consonant-stem nouns (such as , from ) and on the other hand, some i-stem nouns form diminutives in -cul- with no preceding -i- (such as , from ). Synchronically, therefore, the /i/ can be interpreted as part of the suffix (making -iculus an allomorph of -culus) or as a linking vowel.
 * It is preceded by the long vowel /iː/ (-īcul-) in a small number of irregularly formed diminutive nouns (such as from ).
 * It is preceded by the long vowel /eː/ (-ēcul-) in diminutives of fifth declension nouns (such as  from ) and sometimes in diminutives of third declension nouns that have a nominative singular form ending in -ēs (such as  from ).
 * Some diminutives end in . In this context, -s- often represents the original stem-final *s of a word that developed in the oblique stem due to the sound change of rhotacism. (Synchronically, it may also be relevant that stem-final  was usually retained in the nominative singular form of neuter nouns.) From these, the frequent ending  was occasionally extended by analogy to form diminutives of nouns that were not etymologically s-stems; thus, the r-stem nouns  (genitive ) and  (genitive  or ) have diminutives  and, the o-stem noun  (genitive ) has a diminutive , and the ā-stem noun  (genitive ) has a diminutive.
 * N-stem nouns (most of which have nominatives ending in -ō and oblique stems ending in -ōn- or -in-) form diminutives in because of regular sound changes that turned ō or o into u before the cluster /nk/. After -uncul- developed in the diminutives of stems where /n/ was originally preceded by ō or o, this vocalism was extended by analogy to diminutives from n-stem nouns that originally had other vowels before the stem-final /n/ (such as, , diminutive ). Occasionally, the ending  was extended to form diminutives of nouns that were not n-stems.

Examples: