mod·u·lus / ˈmäjələs/ Math. • n. (pl. -li / -ˌlī; -ˌlē/ ) 1. another term for absolute value. ∎ the positive square root of the sum of the squares of the real and imaginary parts of a complex number.2. a constant factor or ratio. ∎ a constant indicating the relation between a physical effect and the force producing it.3. a number used as a divisor for considering numbers in sets, numbers being considered congruent when giving the same remainder when divided by a particular modulus.