Source : Webster's Revised Unabridged Dictionary (1913)

Minus \Mi"nus\, a. [L. See {Minor}, and cf. {Mis-} pref. from
   the French.] (Math.)
   Less; requiring to be subtracted; negative; as, a minus
   quantity.

   {Minus sign} (Math.), the sign [-] denoting minus, or less,
      prefixed to negative quantities, or quantities to be
      subtracted. See {Negative sign}, under {Negative}.

Source : WordNet®

minus sign
     n : a sign indicating the operation of subtraction