synchronic vs coeval

synchronic is not a noun while coeval is a noun.

Word	Noun	Adjective	Verb	Adverb
synchronic	No	Yes	No	No
coeval	Yes	Yes	No	No

synchronic (noun)	coeval (noun)
	a person of nearly the same age as another

synchronic (adjective)	coeval (adjective)
concerned with phenomena (especially language) at a particular period without considering historical antecedents	of the same period
occurring or existing at the same time or having the same period or phase
(of taxa) occurring in the same period of geological time