c.1400, "withdrawal, removal," from L.L. subtractionem (nom. subtractio) "a drawing back, taking away," from L. subtractus, pp. of subtrahere "take away, draw off," from sub "from under" + trahere "to pull, draw" (see tract (1)). The mathematical sense is attested from early
15c. The verb subtract is first recorded c.1540.
"Þou most know þat subtraccion is drawynge of one nowmber oute of anoþer nomber." ["The Crafte of Nombrynge," c.1425]