The term RECIPROCAL OF SINE can be abbreviated to COSEC, which is a five-letter word. COSEC stands for 'co-sine', which is the reciprocal of the sine function in trigonometry. The reciprocal of sine is the inverse of the sine function, meaning that it is the ratio of the hypotenuse to the opposite side of a right triangle. This ratio is used to calculate angles and distances in trigonometric calculations.