a member of an Eastern church that is in union with the Roman Catholic Church, acknowledges the Roman pope as supreme in matters of faith, but maintains its own liturgy, discipline, and rite.
Origin: 1825–35; < Ukrainianuni(y)át, equivalent to úni(ya) the Union of Brest-Litovsk (1596), an acceptance of papal supremacy by some Orthodox clerics in Poland (< Polishuni(j)a < Latinūniōunion) + -(y)at ≪ Latin-ātus-ate1
"pertaining to an Eastern Christian church that acknowledges the supremacy of the Pope," 1833, from Rus. uniyat, from unia "unity, union," from L. unus "one" (see one).