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1580s, "quality of being synchronous," from Modern Latin synchronismus, from Greek synchronismos, from synchronos (see synchronous). Meaning "recurring at the same successive instants of time" is from 1854.
synchronism syn·chro·nism (sĭng'krə-nĭz'əm, sĭn'-)
Coincidence in time; simultaneousness. Also called synchronia.