-unculus

Etymology
Uncommon variant of. The great majority of diminutives that end in the letters were not formed using this suffix; rather, they were formed by adding the diminutive suffix  to the stems of third-declension nouns with nominative singular forms ending in  and oblique stems ending in  or  (such as  (from,  + ) and  (from ,  + )). In these, the ending results from alteration of the vowel before the stem-final  to  due to either regular phonetic sound change (in the case of original  or ) or analogy.

of in the above class of words may be the source of the words where  appears to be used as an independent suffix; alternatively, some words that appear synchronically to have this suffix may have actually been formed originally on an unattested n-stem base (such as ).