quartodeciman

noun

quar·to·dec·i·man

plural -s

usually capitalized : one of a group in the early church especially in Asia Minor who during the 2d century and until the Nicene council in 325 observed Easter on the 14th of Nisan, the day the Jews slaughtered the Passover lamb, regardless of which day of the week that was

: one of the Celtic Christians in the British Isles in the 7th century who followed a different mode of calculating the date of Easter from that used on the continent

Word History

Etymology

Late Latin quartodecimanus, from Latin quartus decimus fourteenth (from quartus fourth + decimus tenth) + -anus -an; akin to Latin quattuor four