A short-term worker's put in double time and endeavour (7)
I believe the answer is:
attempt
'endeavour' is the definition.
('attempt' can be a synonym of 'endeavour')
'a short-term worker's put in double time' is the wordplay.
'short-term worker' becomes 'temp' (I've seen this before).
'put in' is an insertion indicator.
'double' shows that letters should be duplicated.
'time' becomes 't'.
't' doubled is 'tt'.
'temp' inserted into 'tt' is 'ttempt'.
'a'+'ttempt'='ATTEMPT'
'and' acts as a link.
(Other definitions for attempt that I've seen before include "bid to kill someone" , "Tackle" , "Try to climb (a peak)" , "Stab" , "Try, endeavour" .)