tertium quid

ter·ti·um quid  (tûrsh-m kwd, trt-m)

n.

1. Something that cannot be classified into either of two groups considered exhaustive; an intermediate thing or factor.

2. A third person or thing of indeterminate character.

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[Late Latin : Latin tertium, from neuter of tertius, third + quid, something.]

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tertium quid [ˈtɜːtɪəm ˈkwɪd]

n

an unknown or indefinite thing related in some way to two known or definite things, but distinct from both there is either right or wrong, with no tertium quid

[from Late Latin, rendering Greek triton ti some third thing]

Thesaurus

Noun

1.

tertium quid - some third thing similar to two opposites but distinct from both oppositeness, opposition - the relation between opposed entities