TERTIUM QUID

Tertium Quid is regarded as a 'Late Latin' expression.

Much used in the Christian religious controversy of the Fourth Century A.D., it is defined as 'a third something or way that escapes dichotomy categorization'.

Cicero in 'Fam.'9.22.1' wrote: "nihil esse tertium." meaning "There is no third possibility."

In the early Nineteenth Century there was a Tertium Quids political
movement, seemingly resurrected in the Twenty First Century:
http://www.tertiumquids.org/