Sine

or Ricur sine, of an are, in trigonometry, a right line drawn from one extremity. of the arc, perpendicular to the radius drawn to_ the other extremity of it: or, it is half the chord of double the are. Co-sine, is the sine of the complement of an are, So, if an arc be one of 4o degrees, its cosine will be the sine of an arc of 50 degrees.