(Lat. for "shadows," "darkness"), the name for an office sung in Roman Catholic churches on the afternoon or evening of Wednesday, Thursday, and Friday of Holy Week. The name is derived, according to Durandus (Ration., lib. vi. cap. 72, n. 2), from the fact that "the church on these days cultivates darkness (tenebras colit): firstly because it is in sorrow and grief on account of the Lord's Passion, and because for three days it celebrates his exequies since for three days he was dead; secondly, the office of Tenebrae symbolizes the darkness that fell on the face of the earth while the Sun of justice was hung upon the cross," &c. The falling darkness is symbolized by a peculiar and singularly impressive ceremony (see Lights, Ceremonial).