Try case of assault, arresting tense worker (7)
I believe the answer is:
attempt
'try' is the definition.
(synonyms)
'case of assault arresting tense worker' is the wordplay.
'case of' means to remove the middle letters (like emptying a case).
'arresting' indicates putting letters inside.
'tense' becomes 't' (grammatical abbreviation).
'worker' becomes 'temp' (temp is a kind of worker).
'assault' with its middle taken out is 'at'.
't'+'temp'='ttemp'
'at' enclosing 'ttemp' is 'ATTEMPT'.
(Other definitions for attempt that I've seen before include "Endeavor, try" , "Effort; go" , "bid to kill someone" , "Shot" , "Try, make an effort" .)