non·lin·e·ar 
(nŏn-lĭnē-ər)
(nŏn-lĭnē-ər)adj.
1. Not in a straight line.
2. Mathematics
a. Occurring as a result of an operation that is not linear.
b. Containing a variable with an exponent other than one. Used of an equation.
3.
a. Of or relating to a system of equations whose effects are not proportional to their causes. Such a set of equations can be chaotic.
b. Of or relating to a device whose behavior is described by a set of nonlinear equations and whose output is not proportional to its input.
c. Of or relating to the output of such a device.
non·lin′e·ari·ty (-ârĭ-tē) n.