Poem in quarto: delightful (3)
I believe the answer is:
ode
'poem' is the definition.
(I know that ode is a type of rhyme)
'in quarto delightful' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ODE' can be found hidden inside 'quarto delightful'.
(Other definitions for ode that I've seen before include "Poetic composition" , "- - to a 12 Urn" , "Poem expressing noble feelings" , "Lines" , "Verse form" .)