tertium quid

American  

[tur-shee-uhm kwid, ter-ti-oom kwid] / ˈtɜr ʃi əm ˈkwɪd, ˈtɛr tɪˌʊm ˈkwɪd /

noun

1. something related in some way to two things, but distinct from both; something intermediate between two things.

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tertium quid British  

/ ˈtɜːtɪəm ˈkwɪd /

noun

1. 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

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Etymology

Origin of tertium quid

1715–25; < Latin, translation of Greek tríton·ti some third thing

Example Sentences

In this case, this blog is a tertium quid to my other two blogs—it’s related to them but something different altogether.

From Forbes • Jul. 9, 2012

Webb, the tertium quid, is more unlike Chesterton than seems possible.

From Time Magazine Archive

Ironists recalled that for many years Ferdinand and Marie were estranged by a tertium quid, Helene Vacarescu.

From Time Magazine Archive

We can no longer speak of heat and light being reconciled in any tertium quid like wave-motion.

From The Will to Believe : and Other Essays in Popular Philosophy by James, William

That is to say, when two impressions of equal figures are present, there arises in the mind a tertium quid, which is the perception of equality.

From Hume (English Men of Letters Series) by Huxley, Thomas Henry