1953; from synchronic + -ity. Originally in Jung. Synchroneity is from 1889, but equally malformed, and see synchronism.
Entries linking to synchronicity
synchronic adj.
"occurring at the same time," 1775, shortening of synchronical (1650s), from Late Latin synchronus "simultaneous" (see synchronous). Linguistic sense is first recorded 1922, probably a borrowing from French synchronique (de Saussure, 1913). Synchronal "simultaneous" is from 1650s. Related: synchronically.
-ity
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]
synchronism n.
1580s, "quality of being synchronous," from Modern Latin synchronismus, from Greek synkhronismos, from synkhronos (see synchronous). Meaning "recurring at the same successive instants of time" is from 1854.