Measure what goes in pump? (4)
I believe the answer is:
foot
This clue could be a double definition.
'measure' is the first definition.
(foot is a kind of measure)
'goes in pump?' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'what' is the link.
Can you help me to learn more?
(Other definitions for foot that I've seen before include "See 24" , "Metrical unit; pay (a bill)" , "Twelve inches" , "Distance to the end of a limb?" , "12 inches" .)