Unwatered old cattle are well-maintained (4)
I believe the answer is:
neat
'unwatered' is the definition.
(I've seen this in another clue)
'old cattle are well-maintained' is the wordplay.
I cannot quite see how this works, but
'are' could be 'a' (short for 'are', historical unit of measurement) and 'a' is located in the answer.
The remaining letters 'net' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for neat that I've seen before include "without water being added" , "lacking water" , "Elegant - cow (archaic)" , "well-kept" , "Straight - cool!" .)