QUARTODECIMAN

Etymology

Noun

Quartodeciman (plural Quartodecimans)

Any of a group of early Christians who began Easter on Nisan 14, the day Jesus was crucified according to the Gospel of John, and the day before the beginning of Jewish Passover, which is Nisan 15.

Adjective

Quartodeciman (not comparable)

Of or pertaining to these people.

Source: Wiktionary