{ } a. 1. Of, pertaining to, or uttered in, a monotone; monotonous. “Monotonical declamation.” Chesterfield. [ 1913 Webster ]
2. (Math.) Always increasing or always decreasing, as the value of the independent variable increases; -- of a function. [ PJC ]
adj. (Math. or logic) not monotonic; -- of relations between variables. Opposite of monotonic. [ WordNet 1.5 ]