from the GNU version of the Collaborative International Dictionary of English
- adj. the sign -, or minus (opposed in signification to +, or
plus), indicating that the quantity to which it is prefixed is to be subtracted from the preceding quantity, or is to be reckoned from zero or cipher in the opposite direction to that of quanties having the sign plus either expressed or understood; thus, in a - b, b is to be substracted from a, or regarded as opposite to it in value; and -10° on a thermometer means 10° below the zero of the scale.
Sorry, no etymologies found.