Lie about certain free time (7)
I believe the answer is:
leisure
'free time' is the definition.
(I've seen this in another clue)
'lie about certain' is the wordplay.
'about' is an anagram indicator.
'certain' becomes 'sure' (synonyms).
'lie' is an anagram of 'lei'.
'lei'+'sure'='LEISURE'
(Other definitions for leisure that I've seen before include "Rest, relaxation" , "idle hours" , "Freedom from work" , "Time for relaxing" , "Free time as for resting or play" .)