Description of alternative energy for the most part (5)
I believe the answer is:
green
'description' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'alternative energy for the most part' is the wordplay.
'alternative' indicates an anagram.
'for the most part' means to remove the last letter.
'energy' with its final letter taken away is 'energ'.
'energ' anagrammed gives 'GREEN'.
'of' acts as a link.
(Other definitions for green that I've seen before include "member of political party" , ""Go" signal" , "Eg, avocado, emerald" , "Grassy area; naive" , "Lincoln's colour?" .)