He's foppish in an old-fashioned way (7)
I believe the answer is:
coxcomb
This clue could be a double definition.
'he's foppish' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'an old-fashioned way' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'in' is the link.
Can you help me to learn more?
(Other definitions for coxcomb that I've seen before include "Red crest on the head of the domestic fowl" , "Fleshy red crest on a cock's head" , "Fool" , "Popinjay" , "foppish man" .)