Lethargic mole taking cover (6)
I believe the answer is:
sleepy
'lethargic' is the definition.
(I've seen this before)
'mole taking cover' is the wordplay.
'mole' becomes 'spy' (I've seen this before).
'taking' means one lot of letters goes inside another.
'cover' becomes 'lee' (I've seen this in other clues**).
'spy' going around 'lee' is 'SLEEPY'.
(Other definitions for sleepy that I've seen before include "(Of place) low in activity" , "needing a rest" , "Feeling tired" , "Doc's nodding pal" , "Soporific" .)