The first of the brokers has responsibility for extra dividend (5)
I believe the answer is:
bonus
'extra dividend' is the definition.
(I've seen this before)
'the first of the brokers has responsibility' is the wordplay.
'the first of' says to take the initial letters (I've seen 'the first' mean this).
'has' means one lot of letters go next to another.
'responsibility' becomes 'onus' (onus is a duty or responsibility).
The initial letter of 'brokers' is 'b'.
'b'+'onus'='BONUS'
'for' is the link.
(Other definitions for bonus that I've seen before include "Extra payment, may be performance-related" , "Extra payment for good results" , "Perk" , "Sum added to salary for good performance" , "Additional payment to encourage productivity" .)