A stone gets pushed back - it is extremely large (4)
I believe the answer is:
mega
'pushed back it is extremely large' is the definition.
I know nothing about this answer so I can't tell whether this works.
'a stone' is the wordplay.
I cannot really see how this works, but
'a' is within the answer.
The remaining letters 'meg' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'gets' acts as a link.
Can you help me to learn more?
(Other definitions for mega that I've seen before include "Very large (colloq.)" , "Informally great or large" , "Terrific" , "Great American" , "extremely good" .)