Very small but has scope for enlargement (5)
I believe the answer is:
micro
'very small' is the definition.
(I've seen this in another clue)
'has scope for enlargement' is the wordplay.
I cannot quite understand how this works, but
'scope' could be 'cro' (synonyms) and 'cro' is found within the answer.
The remaining letters 'mi' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'but' acts as a link.
Can you help me to learn more?
(Other definitions for micro that I've seen before include "minute" , "Very little" , "needed in kitchen-sink dramas?" , "Prefix meaning tiny, or one-millionth of a unit" , "Prefix meaning very small or one millionth" .)