What does "-osity" mean?

Forming nouns, usually abstract, and usually from adjectives in -ous or -ose.

What is a synonym for "-osity"?

Common synonyms include: ability, hood, ia, ibility, icity, itas → -ity.

/ˈɒ.sɪ.ti/ suffix, slang

suffix, slang ·Moderate ·College level

Suffix

1
Forming nouns, usually abstract, and usually from adjectives in -ous or -ose. morpheme
2
Forming nouns from other adjectives for humorous effect. colloquial, morpheme

From Middle English -ouste, from Old French -ouseté, from Latin -ōsitās; later modified to the current form. It is equivalent to -ose or -ous + -ity.