Cunning writer Umberto pens note in style (3,4)
I believe the answer is:
art deco
'style' is the definition.
(decorative style)
'cunning writer umberto pens note' is the wordplay.
'cunning' becomes 'art' (both can mean artfulness or trickery).
'writer umberto' becomes 'eco' (I've seen this in another clue).
'pens' indicates putting letters inside (inserted letters are held or penned in).
'note' becomes 'D' (musical note).
'art'+'eco'='arteco'
'arteco' going around 'd' is 'ART DECO'.
'in' acts as a link.
(Other definitions for art deco that I've seen before include "Visual design style - redcoat (anag)" , "pre-war style" , "Nineteen twenty's and thirties style" , "Architecture and design movement of the 1930s" , "modern style" .)