COMPLEMENT

COMPLEMENT, in geometry, is what remains of a quadrant of a circle, or of $90^\{\backslash circ\}$, after any certain arch has been taken away from it. Thus, if the arch taken away be $40^\{\backslash circ\}$, its complement is $50^\{\backslash circ\}$: because $50+40=90$. The sine of the complement of an arch is called the cosine, and that of the tangent the cotangent, &c.