A great number got away (4)
I believe the answer is:
vast
'a great' is the definition.
(I've seen this before)
'number got away' is the wordplay.
I cannot quite understand how this works, but
'number' could be 'v' (V is an example) and 'v' is found in the answer.
'away' could be 'a' (abbreviation as used in sports fixtures) and 'a' is found within the answer.
The remaining letters 'st' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for vast that I've seen before include "Huge, enormous" , "Colossal" , "Astronomical" , "Boundless" , "Unusually great" .)