Idle guards lifted sentence in solitary (8)
I believe the answer is:
eremitic
'solitary' is the definition.
(synonyms)
'idle guards lifted sentence' is the wordplay.
'idle' becomes 'eric' (I've seen this before).
'guards' means one lot of letters goes inside another (inserted letters are guarded).
'lifted' says the letters should be written backwards (going up in down clue).
'sentence' becomes 'time' (a prison sentence).
'time' back-to-front is 'emit'.
'eric' enclosing 'emit' is 'EREMITIC'.
'in' acts as a link.
(Another definition for eremitic that I've seen is " Solitary".)