Rear section of orchestra is effective (5)
I believe the answer is:
raise
'rear' is the definition.
(I know that rear can be written as raise)
'section of orchestra is effective' is the wordplay.
'section of' says the answer is hidden in the clue.
'RAISE' can be found hidden inside 'orchestra is effective'.
(Other definitions for raise that I've seen before include "Increased earnings in America" , "Wage increase" , "Bring up - an increase in pay" , "To promote" , "climb" .)