mid-14c., multiplicacioun, "any increase in size, number, or amount; act or process of increasing in number," from Old French multiplicacion (12c.) "multiplication, duplication; multiplicity, diversity," from Latin multiplicationem (nominative multiplicatio), noun of action from past-participle stem of multiplicare "to multiply, increase" (see multiply). The arithmetical sense of "process in which one number is considered as an operator on another" is attested from late 14c.