You couldn't really have got half soused on one! (3)
I believe the answer is:
sou
'half soused on one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'you couldn't really have' is the wordplay.
I cannot quite see how this works, but
'you' could be 'u' (homophones) and 'u' is located in the answer.
'really' could be 'so' (both can mean 'extremely') and 'so' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'got' is the link.
Can you help me to learn more?
(Other definitions for sou that I've seen before include "Five-centime piece" , "Former small French coin" , "Very little to spend" , "Old French coin of little value" , "Old French monetary unit" .)