Natural environment welcoming check on energy (9)
I believe the answer is:
ecosystem
'natural' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'environment welcoming check on energy' is the wordplay.
'environment welcoming' becomes 'cosy' (I am not sure about this - if you are sure you should believe this answer much more).
'check' becomes 'stem' (both can mean to control or stop).
'on' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mco).
'cosy'+'stem'='cosystem'
'cosystem' after 'e' is 'ECOSYSTEM'.
Can you help me to learn more?
(Other definitions for ecosystem that I've seen before include "orderly collection of organisms" , "The interaction of a group of organisms with their physical environment" , "Community of organisms and their environment" , "integrated community" , "Biological community with its environment" .)