nocturn
Concise Oxford English Dictionary © 2008 Oxford University Press:
nocturn/ˈnɒktəːn/
▶noun (in the Roman Catholic Church) a part of matins originally said at night.
– origin ME: from OFr. nocturne or eccles. L. nocturnum, neut. of L. nocturnus ‘of the night’.
'nocturn' also found in these Oxford entries:

