Ounce captured by farmer who likes a drink (6)
I believe the answer is:
boozer
'farmer who likes a drink' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'ounce captured by' is the wordplay.
'ounce' becomes 'oz'.
'captured' indicates putting letters inside.
'by' becomes 'boer' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'oz' going within 'boer' is 'BOOZER'.
Can you help me to learn more?
(Other definitions for boozer that I've seen before include "Pub (slang)" , "Pub (sl.)" , "Inn" , "Heavy drinker" .)