Used on watch? (6,4)
I believe the answer is:
second hand
This might be a double definition.
'used' is the first definition.
(I know that used can be written as second-hand)
'watch?' is the second 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 don't see?
'on' acts as a link.
Can you help me to learn more?
(Other definitions for second hand that I've seen before include "Watch component" , "Pointer on dial" , "Previously owned - part of watch" , "Part of a timepiece" , "going quickly on the clock?" .)