Highlight money on account (6)
I believe the answer is:
accent
'highlight' is the definition.
(I've seen this in another clue)
'money on account' is the wordplay.
'money' becomes 'cent' (eg denomination of dollars).
'on' means one lot of letters go next to another.
'account' becomes 'ac' (abbreviation for account).
'cent' put after 'ac' is 'ACCENT'.
(Other definitions for accent that I've seen before include "Stress - regional dialect" , "Stress - manner of speech" , "Distinctive local way of speaking" , "intensity" , "Speech inflection" .)