A cuff on the wrist (7)
I believe the answer is:
manacle
This could be a double definition.
'a cuff' is the first definition.
('manacle' can be a synonym of 'cuff')
'the wrist' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'on' acts as a link.
Can you help me to learn more?
(Other definitions for manacle that I've seen before include "restricting at the cuff?" , "Metal shackle" , "Curb" , "Shackle on the wrist" , "Handcuff" .)