Relative sat around before lack of activity (6)
I believe the answer is:
stasis
'lack of activity' is the definition.
(I've seen this in another clue)
'relative sat around before' is the wordplay.
'relative' becomes 'sis' (short for sister).
'around' indicates anagramming the letters.
'before' is a charade indicator (letters next to each other).
'sat' anagrammed gives 'sta'.
'sis' after 'sta' is 'STASIS'.
(Other definitions for stasis that I've seen before include "State in which blood-flow is stopped" , "Inactivity or stoppage of circulation" , "Standstill" , "lack of progress" , "Cessation" .)