Ball and socket (4)
I believe the answer is:
jack
This could be a double definition.
'ball' is the first definition.
(type of ball in bowls)
'socket' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'and' acts as a link.
Can you help me to learn more?
(Other definitions for jack that I've seen before include "Target ball in bowls" , "Raise" , "Car-lifting tool" , "Lifting device - flag - boy's name - card - fish" , "Dog akin to 9" .)