Pass by old girl leaning back — really large (8)
I believe the answer is:
colossal
'large' is the definition.
(similar in meaning)
'pass by old girl leaning back really' is the wordplay.
'pass' becomes 'col' (col is a term for a mountain pass).
'by' says to put letters next to each other.
'old girl leaning' becomes 'sal' (I can't explain this - if you can you should believe this answer much more).
'back' says the letters should be written in reverse.
'really' becomes 'so' (both can mean 'extremely').
'so' written backwards gives 'os'.
'sal' after 'os' is 'ossal'.
'col'+'ossal'='COLOSSAL'
Can you help me to learn more?
(Other definitions for colossal that I've seen before include "Stupendous" , "Huge, vast" , "Jumbo" , "Huge, immense" , "Very big" .)