King abandons Lancelot for one dark period (5)
I believe the answer is:
night
'dark period' is the definition.
(period of the day when it's dark)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for night that I've seen before include "Darkness; see you in the morning" , "End of the day" , "The dark time" , "Time between days" , "Tennyson's "black bat"" .)