Be very busy, certain to hitch up something off the shoulder (7)
I believe the answer is:
humerus
'the shoulder' is the definition.
The definition and answer can be both body parts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'be very busy certain to hitch up something' is the wordplay.
I cannot really see how this works, but
'be' could be 'hum' (humming is a kind of being) and 'hum' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'off' is the link.
Can you help me to learn more?
(Other definitions for humerus that I've seen before include "Bone from shoulder to elbow" , "Bone that sounds funny?" , "Arm bone (that sounds comical)" , "Arm bone - the "funny bone"" , "Upper-arm bone" .)