It's singularly useful when you want to hold hands (7)
I believe the answer is:
manacle
'hold hands' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for manacle that I've seen before include "Shackle on the wrist" , "Metal shackle" , "Curb" , "Handcuff" , "item restricting movement" .)