Ulnar nerve (5,4)
I believe the answer is:
funny bone
'ulnar nerve' is the definition.
(I know that ulnar nerve can be written as funny bone)
This is all the clue.
(Other definitions for funny bone that I've seen before include "Part of elbow with sensitive nerve - hilarious" , "found up one's sleeve" , "Humerus" , "part of arm" , "exposed nerve" .)