1 a moonlit night 20.
2 good night 19. etymology: been ‘fine, good, costly rich, gentle’ + darkment a Cant term for ‘night’; attested by BS in TDITA; collected by EMcC/PS note:
Grose and Egan (1823) attest sense 2 as ‘Cant’.
Canadian Paul Pope (2013) cites the form bene darkment and he defines it as ‘moonlight night, good night’.