A judge can do it up (3)
I believe the answer is:
sum
'a judge can' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for sum that I've seen before include "Amount, aggregate" , "Amount of money; add" , "An additional problem" , "Amount, of money say" , "Amount of money; total" .)