Listener's bottom pain returned -- it's growing (7)
I believe the answer is:
lobelia
'growing' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'listener's bottom pain returned' is the wordplay.
'listener's bottom' becomes 'lobe' (I can't justify this - if you can you should give a lot more credence to this answer).
'pain' becomes 'ail' (synonyms).
'returned' says the letters should be written in reverse.
'ail' in reverse letter order is 'lia'.
'lobe'+'lia'='LOBELIA'
'it's' is the link.
Can you help me to learn more?
(Other definitions for lobelia that I've seen before include "Tropical or subtropical bedding plant" , "Lo, I bale out the flower" , "Flower used for hanging baskets" , "Showy garden flower" , "Common garden flower" .)