any of the days in the quarterly three-day period of prayer and fasting (the Wednesday, Friday, and Saturday after the first Sunday in Lent, after Whitsunday, after Sept. 14, and after Dec. 13) observed in the Roman Catholic Church and other Western churches.
[ bef. 1050; ME ymber day, OE ymbrendaeg, pl. -dagas, equiv. to ymbryne recurrence ( ymb ( e ) around + ryne a running) + daeg DAY ]