Cover over most of Scottish county, being sluggish (7)
I believe the answer is:
languid
'sluggish' is the definition.
('languid' can be a synonym of 'sluggish')
'cover over most of scottish county' is the wordplay.
'cover' becomes 'lid' (lid is a kind of cover**).
'over' means one lot of letters goes inside another.
'most of' means to remove the last letter.
'scottish county' becomes 'angus' (I've seen this before).
'angus' with its last letter taken away is 'angu'.
'lid' placed around 'angu' is 'LANGUID'.
'being' acts as a link.
(Other definitions for languid that I've seen before include "Sluggish" , "Lacking spirit or liveliness" , "Slow" , "Idolent, lacking vitality" , "... flagging" .)