The style of many a poem (4)
I believe the answer is:
mode
'the style' is the definition.
('mode' can be a synonym of 'style')
'many a poem' is the wordplay.
'many' becomes 'm' (**).
'a poem' becomes 'ode' (ode is a kind of poem).
'm'+'ode'='MODE'
'of' acts as a link.
(Other definitions for mode that I've seen before include "Way, style" , "Fashion; manner" , "Style, method" , "Trend" , "Way of doing something" .)