Pieces of silicon hooped over end of bicycle pump? (4)
I believe the answer is:
shoe
'pump?' is the definition.
(pump is a kind of shoe)
'pieces of silicon hooped over end of bicycle' is the wordplay.
'pieces of' indicates taking the first letters.
'end of' says to take the final letters.
The initial letters of 'silicon hooped over' is 'sho'.
The final letter of 'bicycle' is 'e'.
'sho'+'e'='SHOE'
(Other definitions for shoe that I've seen before include "'For want of a nail the . . . . was lost'" , "Case for cards in a casino" , "Rim of metal nailed to a horse's hoof" , "Sandal or brogue?" , "Footwear - playing-card dispenser - part of a brake" .)