† ˈfactusMath.Obs.rare. [a. L. factus (? sc.numerus), pa.pple.masc. of facĕre to make.] The product of two or more numbers or expressions; = factum 3. 1669Newton in Rigaud Cor.Sci. Men II. 282 The factus of their denominators will be b5 + 10 b4 + 35 b3 + 50 bb + 24 b.