Huge growth in socialist club (7)
I believe the answer is:
redwood
'huge growth' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'socialist club' is the wordplay.
'socialist' becomes 'red' (red can informally mean a socialist).
'club' becomes 'wood' (wood is a kind of club).
'red'+'wood'='REDWOOD'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for redwood that I've seen before include "Tory MP" , "Californian conifer" , "Giant tree of California" , "former Tory minister" , "Giant American tree" .)