Fashion Frenchman a poem (4)
I believe the answer is:
mode
'fashion' is the definition.
('mode' can be a synonym of 'fashion')
'frenchman a poem' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'a poem' becomes 'ode' (ode is a kind of poem).
'm'+'ode'='MODE'
(Other definitions for mode that I've seen before include "Manner of dome" , "Way, style" , "Style, method" , "Style (of clothes, etc)" , "Fashion; way of performing" .)