Endeavour, try (7)
I believe the answer is:
attempt
This clue is a double definition.
'endeavour' is the first definition.
(synonyms)
'try' is the second definition.
(I know that try can be written as attempt)
(Other definitions for attempt that I've seen before include "Effort; go" , "bid to kill someone" , "Tackle" , "Try to climb (a peak)" , "Shot" .)