Such a piece would be pretty, I imagine (5)
I believe the answer is:
fancy
'imagine' is the definition.
(fancying is a kind of imagining)
'such a piece would be pretty i' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fancy that I've seen before include "Elaborate; whim" , "idea" , "Unfounded belief" , "Imagine - find attractive" , "Imagine; desire" .)