1. a sign indicating the operation of subtraction;

The Collaborative International Dictionary of English v.0.48:

Minus \Mi"nus\ (m[imac]"n[u^]s), a. [L. See Minor, and cf. Mis- pref. from the French.] (Math.) Less; requiring to be subtracted; negative; as, a minus quantity. [1913 Webster] Minus sign (Math.), the sign [-] denoting minus, or less, prefixed to negative quantities, or quantities to be subtracted. See Negative sign, under Negative. [1913 Webster]WordNet (r) 3.0 (2006):

minus sign n 1: a sign indicating the operation of subtraction