Eccentric Scotsman standing on head (3)
I believe the answer is:
cam
'eccentric' is the definition.
(an eccentric is a mechanical device such as a cam)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cam that I've seen before include "running through university city?" , "Projection on a rotating shaft in contact with another part" , "English river" , "Reciprocal-motion part" , "Part of engine" .)