Tenebrae
Concise Oxford English Dictionary © 2008 Oxford University Press:
Tenebrae /ˈtɛnɪbriː, -breɪ/
▶plural noun (in the Roman Catholic Church) matins and lauds for the last three days of Holy Week, at which candles are successively extinguished.
– origin L., lit. ‘darkness’.
'Tenebrae' also found in these Oxford entries:

