1. designating or involving an equation whose terms are not of the first degree;

The Collaborative International Dictionary of English v.0.48:

nonlinear \nonlinear\ adj. 1. (Math.) Not depictable graphically as a straight line; not changing by a constant amount for each unit of time, distance, or other independent variable. Opposite of linear. [WordNet 1.5 +PJC] 2. (Math.) Containing variables of greater than the first degree; -- of an equation. Opposite of linear. [PJC] 3. (Physics) Represented by equations containing variables of greater than the first degree; -- of physical processes or relationships. Opposite of linear. [PJC]WordNet (r) 3.0 (2006):

nonlinear adj 1: designating or involving an equation whose terms are not of the first degree [ant: additive, linear]The Jargon File (version 4.4.7, 29 Dec 2003):

nonlinear adj. [scientific computation] 1. Behaving in an erratic and unpredictable fashion; unstable. When used to describe the behavior of a machine or program, it suggests that said machine or program is being forced to run far outside of design specifications. This behavior may be induced by unreasonable inputs, or may be triggered when a more mundane bug sends the computation far off from its expected course. 2. When describing the behavior of a person, suggests a tantrum or a flame . ?When you talk to Bob, don't mention the drug problem or he'll go nonlinear for hours.? In this context, go nonlinear connotes ?blow up out of proportion? (proportion connotes linearity).The Free On-line Dictionary of Computing (30 December 2018):

nonlinear (Scientific computation) A property of a system whose output is not proportional to its input. For example, a transistor has a region of input voltages for which its output voltage is found by multiplying the input voltage by the gain of the transistor. Outside this region though, the transistor behaves non-linearly, meaning that it does not obey this simple equation. The behaviour of a system containing non-linear components is thus harder to model and to predict. [Jargon File]