Many a poem has style (4)
I believe the answer is:
mode
'style' is the definition.
(I know that style can be written as mode)
'many a poem' is the wordplay.
'many' becomes 'm' (Roman numeral for a thousand).
'a poem' becomes 'ode' (ode is a kind of poem).
'm'+'ode'='MODE'
'has' is the link.
(Other definitions for mode that I've seen before include "Way of operation" , "Custom" , "Trend" , "Style, method" , "Style (of clothes, etc)" .)