community (n.)youdaoicibaDictYouDict[community 词源字典]
late 14c., from Old French comunité "community, commonness, everybody" (Modern French communauté), from Latin communitatem (nominative communitas) "community, society, fellowship, friendly intercourse; courtesy, condescension, affability," from communis "common, public, general, shared by all or many," (see common (adj.)). Latin communitatem "was merely a noun of quality ... meaning 'fellowship, community of relations or feelings,' but in med.L. it was, like universitas, used concretely in the sense of 'a body of fellows or fellow-townsmen' " [OED].

An Old English word for "community" was gemænscipe "community, fellowship, union, common ownership," from mæne "common, public, general," probably composed from the same PIE roots as communis. Community service as a criminal sentence is recorded from 1972, American English. Community college is recorded from 1959.[community etymology, community origin, 英语词源]
-ityyoudaoicibaDictYouDict
suffix forming abstract nouns from adjectives, meaning "condition or quality of being ______," from Middle English -ite, from Old French -ité and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of connective -i- + -tas (see -ty (2)).
Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]