Meaning

adjective occurring or existing at the same time or having the same period or phase; - Jour.A.M.A.

adjective concerned with phenomena (especially language) at a particular period without considering historical antecedents

adjective (of taxa) occurring in the same period of geological time

originBy surface analysis, syn- + chron- + -ic; historically, see synchronous § Etymology.

Etymology from Wiktionary, CC BY-SA 3.0