Lie about certain time off work (7)
I believe the answer is:
leisure
'time off work' is the definition.
(I've seen this before)
'lie about certain' is the wordplay.
'about' indicates an anagram.
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'lie' with letters rearranged gives 'lei'.
'lei'+'sure'='LEISURE'
(Other definitions for leisure that I've seen before include "Free-time" , "idle hours" , "Convenient opportunity" , "retirement" , "Rest, relaxation" .)