subcontrary

adjective

1. Contrary in an inferior degree. (logic) Denoting the relation of opposition between the particular affirmative and particular negative. Of these both may be true and only one can be false.

2. (geometry) Having, or being in, a contrary order; said of a section of an oblique cone having a circular base made by a plane not parallel to the base, but so inclined to the axis that the section is a circle; applied also to two similar triangles when so placed as to have a common angle at the vertex, the opposite sides not being parallel.

3. (logic) Denoting the relation of opposition between the particular affirmative and particular negative. Of these both may be true and only one can be false.

noun

1. (logic) Either of a pair of propositions at least one of which must be true