The term SINE OR COSINE is a mathematical concept that refers to two of the three main trigonometric functions. The sine and cosine functions are used to describe the relationship between the angles of a triangle and the lengths of its sides. The RATIO of the length of one side of a triangle to the length of another side is known as the sine or cosine of the angle between them. The crossword solution for this term is RATIO, which is an appropriate answer since it describes the relationship between the sides of a triangle.