Good sort meeting Green: minister once (5)
I believe the answer is:
straw
'good sort' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'meeting green minister once' is the wordplay.
'meeting' means one lot of letters go next to another.
'green' becomes 'raw' (both can mean naive or inexperienced).
'minister once' becomes 'st' (I am not sure about this - if you are sure you should believe this answer much more).
'raw' after 'st' is 'STRAW'.
Can you help me to learn more?
(Other definitions for straw that I've seen before include "Dry stalk of grain" , "Warts (anag.)" , "Pale yellow colour" , "Animal bedding" , "Residue of threshed corn" .)