Habitual tumbler, jockey gets third knocking to head (5)
I believe the answer is:
drier
'head' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for drier that I've seen before include "increasingly teetotal" , "More dull" , "Less moist" , "Laundry machine" , "Machine which removes water" .)