Quasilinear may refer to: Quasilinear function, a function that is both quasiconvex and quasiconcave Quasilinear utility, an economic utility function linear in one argument In complexity theory and mathematics, O(n log n) or sometimes O(n (log n)k) Quasilinear equation, a type of differential equation where the coefficient(s) of the highest order derivative(s) of the unknown function do not depend on highest order derivative(s)