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ter·ti·um quid(tûr′shē-əm kwĭd′, tĕr′tē-o͝om′)
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.
[Late Latin : Latin tertium, from neuter of tertius, third + quid, something.]
tertium quid(ˈtɜːtɪəm ˈkwɪd)
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.
[C18: from Late Latin, rendering Greek triton ti some third thing]
ter•ti•um quid(ˈtɜr ʃi əm ˈkwɪd, ˈtɛər ti-)
1. something related in some way to two things, but distinct from both; something intermediate between two things.
2. a third person or thing of indeterminate character.
[1715–25; < Latin, translation of Greek tríton ti some third thing]