adjective

1. (of a binary relation R on a set S) Having the property that, for any two distinct elements of S, at least one is not related to the other via R; equivalently, having the property that, for any x, y ∈ S, if both xRy and yRx then x=y.

2. (of certain mathematical objects) Whose sign changes on the application of a matrix transpose or some generalisation thereof: