early 15c., "pleasant," from Late Latin amicabilis "friendly," a word in Roman law, from Latin amicus "friend," ultimately from amare "to love" (see Amy). In modern use "characterized by friendliness, free from hard feelings, peaceable, socially harmonious." Compare amiable, which is the same word through French. Related: Amicableness.
word-forming element making abstract nouns from adjectives and meaning "condition or quality of being ______," from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -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]
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Definitions of amicability from WordNet
a disinclination to quarrel;
having a disposition characterized by warmth and friendliness;