adj. 1. (of a number) exactly divisible by two; equal to 2n for some integer n. Thus the even numbers form the infinite sequence 2, 4, 6, 8,... 2. (of a function) changing neither sign nor absolute value when the sign of the independent variable is changed, so that f(x) = f(-x). The graph of such a function is thus symmetrical about the y-axis, as illustrated by the graph of the cosine function shown in Cosx is an even function. 3. (of a permutation) derivable from the natural ordering by an even number of exchanges of single elements. For example, (3 1 2) is derived from (1 2 3) by exchanging 3 and 1 and then 3 and 2, but (1 3 2) requires an odd number of such pairwise exchanges. See also difference polynomial. Compare odd. See also parity.