Joint that's swinging? (5)
I believe the answer is:
hinge
This clue might be a double definition.
'joint' is the first definition.
(type of joint)
'swinging?' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for hinge that I've seen before include "Key principle" , "Part of a door" , "Circumstance upon which subsequent events depend; door facilitator" , "Door support" , "Pivotal point" .)