Persist in questioning footwear (4)
I believe the answer is:
pump
'footwear' is the definition.
(I know that pump is a type of shoe)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for pump that I've seen before include "Flat shoe; siphon" , "Fluid moving device" , "The heart is one" , "Compressor, light shoe" , "Shoe - inflating device" .)