"To a ..." poem (3)
I believe the answer is:
ode
'to a poem' is the definition.
(ode is a type of poem)
This is the entire clue.
(Other definitions for ode that I've seen before include "Lines" , "Poem in praise of doe" , "Verse form" , "- - to a 12 Urn" , "(Railway)system" .)