A piece of poetry (6)
I believe the answer is:
stanza
'a piece of poetry' is the definition.
(group of lines in a poem)
'a piece' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stanza that I've seen before include "Component of poem" , "A verse of poetry" , "Poetic unit" , "Verse of poem" , "Poetic verse" .)