co-eˈffect [co- 3 a.] A joint or concomitant effect. 1768–74Tucker Lt. Nat. (1852) I. 34 Discernment is not the cause but concomitant of action, or co-effect of the same cause.1778Phil.Trans. LXVIII. 490 We shall be embarassed by the degrees of these co-effects.