Stress that money is on account (6)
I believe the answer is:
accent
'stress' is the definition.
(accent can mean to emphasise or stress)
'money is on account' is the wordplay.
'money' becomes 'cent' (eg denomination of dollars).
'is on' says to put letters next to each other.
'account' becomes 'ac' (abbreviation for account).
'cent' after 'ac' is 'ACCENT'.
'that' acts as a link.
(Other definitions for accent that I've seen before include "Emphasis on syllable or local pronunciation" , "Speech pattern" , "Regional speech characteristic" , "Emphasis on syllabus or word" , "Mark over a vowel, perhaps" .)