tenebrae

noun (used with a singular or plural verb) Roman Catholic Church.

1. the office of matins and lauds for Thursday, Friday, and Saturday of Holy Week, sung respectively on the afternoon of Wednesday, Thursday, and Friday of that week, at which the Crucifixion is commemorated by the gradual extinguishment of candles.

noun

1. (functioning as singular or plural) RC Church (formerly) the matins and lauds for Thursday, Friday, and Saturday of Holy Week, usually sung in the evenings or at night