a Holy Week night service (Wednesday through Friday), formerly widely observed in the Western Church, consisting of group recitation of Matins and Lauds of the following day in commemoration of Christ's death and burial
L, pl., shadows, darkness: see temerity
See Tenebrae in American Heritage Dictionary 4
plural noun Roman Catholic Church(used with a sing. or pl. verb)
The office of matins and lauds sung on the last three days of Holy Week, with a ceremony of candles.