Short poem on a disc (7)
I believe the answer is:
roundel
This clue could be a double definition.
'short poem' is the first definition.
'roundel' can be an answer for 'poem' (roundel is a kind of poem). I am unsure of the 'short' bit.
'disc' is the second definition.
(I have seen 'Coloured disc ' mean 'roundel' so perhaps 'disc' could also mean 'roundel')
'on a' is the link.
Can you help me to learn more?
(Other definitions for roundel that I've seen before include "Circle identifying aircraft" , "Small circular window or design" , "Circular insignia (on military aircraft)" , "Refrain" , "Circular marking on RAF plane" .)