Reward note on responsibility (5)
I believe the answer is:
bonus
'reward' is the definition.
(thesaurus)
'note on responsibility' is the wordplay.
'note' becomes 'b' (musical note).
'on' says to put letters next to each other.
'responsibility' becomes 'onus' (I've seen this before).
'b'+'onus'='BONUS'
(Other definitions for bonus that I've seen before include "bribe" , "Perk" , "Extra payment, may be performance-related" , "Additional wage" , "Tip" .)