Conjugate axis of a hyperbola (Math.), the line through the center of the curve, perpendicular to the line through the two foci. -- Conjugate diameters (Conic Sections), two diameters of an ellipse or hyperbola such that each bisects all chords drawn parallel to the other. -- Conjugate focus (Opt.) See under Focus. -- Conjugate mirrors (Optics), two mirrors so placed that rays from the focus of one are received at the focus of the other, especially two concave mirrors so placed that rays proceeding from the principal focus of one and reflected in a parallel beam are received upon the other and brought to the principal focus. -- Conjugate point (Geom.), an acnode. See Acnode, and Double point. -- Self-conjugate triangle (Conic Sections), a triangle each of whose vertices is the pole of the opposite side with reference to a conic.

We have learned, in logic, that conjugates are sometimes in name only, and not in deed.
Abp. Bramhall.