Old-fashioned you, having S&M! (8)
I believe the answer is:
thousand
'old-fashioned' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I don't see?
'you having sm' is the wordplay.
'you' becomes 'thou' (historical second person pronoun).
'having sm' becomes 'sand' (I can't justify this - if you can you should give a lot more credence to this answer).
'thou'+'sand'='THOUSAND'
(Other definitions for thousand that I've seen before include "Ten hundred" , "Ten cubed" , "Large number" , "a fair amount?" , "Grand" .)