subcontrary

sub- +‎ contrary

subcontrary (not comparable)

1. Contrary in an inferior degree.
   1. (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.

      (Can we find and add a quotation of Brande & C to this entry?)

   2. (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.

subcontrary (plural subcontraries)

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