When teaching precalculus, I must take pains to disambiguate two homophones which have even been known to occur in the same sentence. One of them is defined early in the course as the ratio, in a right triangle, of the side opposite a given angle to the hypotenuse. Later on, the definition of this first word is extended to involve circles -- and that's when the second word becomes a lot more relevant. What is the second word?

SIGN