1. (a.) Existing at the same time with another.

2. (n.) That which coexists with another.

accompanying accordant affirmative agreeable agreeing answerable at one coetaneous coeternal coeval coexisting coherent coincident coinciding coinstantaneous collateral commensurate compatible concomitant concordant concurrent concurring conformable congenial congruent congruous consentaneous consentient consistent consonant contemporaneous contemporary conterminous cooperating cooperative correspondent corresponding coterminous en rapport equivalent harmonious in accord in agreement in rapport in sync in synchronization inaccordance inharmony isochronal isochronous like-minded of a piece of like mind of one mind on all fours positive proportionate reconcilable self-consistent simultaneous symbiotic synchronal synchronic synchronized synchronous unanimous uniform unison unisonant unisonous