-ulus

Cognate with Proto-Germanic *-ilaz and *-ulaz, whence no longer productive English -le (as in dimple and nozzle), Dutch -el, German -el.

(Classical) IPA^(key): /u.lus/, [ʊɫ̪ʊs̠]
(modern Italianate Ecclesiastical) IPA^(key): /u.lus/, [ulus] (stressed on the antepenult)

-ulus (feminine -ula, neuter -ulum); first/second-declension suffix

Used to form a diminutive of a noun, indicating small size or youth.
Used to form a diminutive of an adjective with diminished effect, indicating “somewhat” or “-ish”.
Used to form an agent noun or adjective from a verb.

The suffix -ulus is added to a noun to form a diminutive of that noun. Latin diminutives typically match the gender of the base word.

Examples:

‎rēx m (“king”) + ‎-ulus → ‎rēgulus m (“prince, petty king”)

‎virga f (“twig, rod, switch, staff”) + ‎-ulus → ‎virgula f (“little twig, small rod, wand”)

‎oppidum n (“town, settlement”) + ‎-ulus → ‎oppidulum n (“small town or settlement, village”)

‎calx f (“limestone, game counter”) + ‎-ulus → ‎calculus m (“pebble, little stone”)

The allomorph -olus, -ola, -olum is regularly used to form diminutives of nouns ending in -ius, -ia, -ium, -eus, -ea, -eum.

When added to an adjective, it forms a diminutive of that adjective:

‎albus (“white”) + ‎-ulus → ‎albulus (“whitish”, literally “a little white”)

When added to a verb, it forms an adjective with the relational meaning “doing …” or “tending to …”:

‎tremō (“tremble”) + ‎-ulus → ‎tremulus (“trembling, tending to tremble”)

‎crēdō (“believe”) + ‎-ulus → ‎crēdulus (“believing, tending to believe”)

Case / Gender	Masculine	Feminine	Neuter	Masculine	Feminine	Neuter
Number	Singular			Plural
Nominative	-ulus	-ula	-ulum	-ulī	-ulae	-ula
Genitive	-ulī	-ulae	-ulī	-ulōrum	-ulārum	-ulōrum
Dative	-ulō	-ulae	-ulō	-ulīs
Accusative	-ulum	-ulam	-ulum	-ulōs	-ulās	-ula
Ablative	-ulō	-ulā	-ulō	-ulīs
Vocative	-ule	-ula	-ulum	-ulī	-ulae	-ula