Rest when idle, now labouring (3-4)
I believe the answer is:
lie-down
'rest' is the definition.
(to lie down is to have a short rest)
'idle now labouring' is the wordplay.
'labouring' is an anagram indicator (letters worked or laboured into a new form).
'idle'+'now'='idlenow'
'idlenow' is an anagram of 'LIE-DOWN'.
'when' is the link.
(Other definitions for lie-down that I've seen before include "Short rest" , "Rest (with or without sleep)" .)