Allow, but with constraint (3)
I believe the answer is:
let
This clue might be a double definition.
'allow' is the first definition.
(I know that allow is a more specific form of allow)
'with constraint' is the second definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'but' is the link.
Can you help me to learn more?
(Other definitions for let that I've seen before include "Permitted" , "hired" , "Allow on the tennis court" , "Service that must be repeated" , "Allowed or rented out" .)