In darkness one circles lake (5)
I believe the answer is:
unlit
'in darkness' is the definition.
(I've seen this in another clue)
'one circles lake' is the wordplay.
'one' becomes 'unit' (synonyms).
'circles' indicates putting letters inside.
'lake' becomes 'L' (geographical abbreviation).
'unit' placed around 'l' is 'UNLIT'.
(Other definitions for unlit that I've seen before include "Dark, gloomy" , "Not illuminated" , "not provided with a lamp?" , "Until (anag.)" , "Without illumination" .)