in·co·her·ent / ˌinkōˈhi(ə)rənt; ˌing-; -ˈher-/ • adj. 1. (of spoken or written language) expressed in an incomprehensible or confusing way; unclear: he screamed some incoherent threat. ∎ (of a person) unable to speak intelligibly: I splutter several more times before becoming incoherent. ∎ (of an ideology, policy, or system) internally inconsistent; illogical: the film is ideologically incoherent.2. Physics (of waves) having no definite or stable phase relationship.DERIVATIVES: in·co·her·ence n.in·co·her·en·cy n. (pl. -cies) in·co·her·ent·ly adv.