Firm kiss for a coin (6)
I believe the answer is:
copeck
'for a coin' is the definition.
(I've seen this before)
'firm kiss' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'kiss' becomes 'peck' (pecking is a kind of kissing).
'co'+'peck'='COPECK'
(Other definitions for copeck that I've seen before include "small change in Russia" , "In Russia it is tender" , "Russian coin" , "money of little value" , "little change in Russia" .)