subcontrary

[suhb-kon-trer-ee] /sʌbˈkɒn trɛr i/
noun, plural subcontraries. Logic.
1.
one of two propositions that can both be true but cannot both be false.
Origin
1595-1605; < Medieval Latin subcontrārius, Late Latin (see sub-, contrary), orig. as translation of Greek hypenantíos
British Dictionary definitions for subcontrary

subcontrary

/sʌbˈkɒntrərɪ/
adjective
1.
(of a pair of propositions) related such that they cannot both be false at once, although they may be true together Compare contrary (sense 5), contradictory (sense 3)
noun (pl) -ries
2.
a statement that cannot be false when a given statement is false