minus (n.) Look up minus at Dictionary.com
1650s, from minus (prep.).
minus (prep.) Look up minus at Dictionary.com
late 15c., "with subtraction of," from Latin minus "less," neuter of minor "smaller," from PIE *mi-nu-, suffixed form of root *mei- (2) "small" (source also of Latin minuere "to diminish, reduce, lessen," Greek meion "less, smaller," Old English minsian "to diminish," Sanskrit miyate "diminishes, declines," Russian men'she "less").

Mathematical use in expressions of calculation did not exist in the word in classical Latin and is probably from North Sea medieval commercial usage of Latin plus and minus to indicate surplus or deficiency of weight or measure. Origin of the "minus sign" is disputed.