Big and growing, Edward lacks a way to enter the back door (7)
I believe the answer is:
redwood
'big and growing' is the definition.
I can't judge whether this defines the answer.
'edward lacks a way to enter the back door' is the wordplay.
'edward' becomes 'Ed' (short for Edward).
'lacks a way' becomes 'w' (I am not sure about this - if you are sure you should believe this answer much more).
'to enter' indicates putting letters inside.
'the back' says the letters should be written backwards.
'door' written backwards gives 'rood'.
'ed'+'w'='edw'
'edw' placed inside 'rood' is 'REDWOOD'.
Can you help me to learn more?
(Other definitions for redwood that I've seen before include "former Tory minister" , "Tory MP" , "Large American tree" , "Very tall tree" , "may be growing in California" .)