Charge on account for buttonhole (6)
I believe the answer is:
accost
'for buttonhole' is the definition.
(both can mean to detain in conversation)
'charge on account' is the wordplay.
'charge' becomes 'cost' (I've seen this in another clue).
'on' says to put letters next to each other.
'account' becomes 'ac' (abbreviation for account).
'cost' after 'ac' is 'ACCOST'.
(Other definitions for accost that I've seen before include "such as a solicitor might do" , "Make bold approach to" , "Approach boldly or insolently" , "Come up and address" , "Approach and address boldly" .)