Deceleration device to snap we hear (5)
I believe the answer is:
brake
'deceleration device' is the definition.
'brake' can be an answer for 'device' (brake is a kind of device). I am unsure of the 'deceleration' bit.
'snap we hear' is the wordplay.
'snap' becomes 'break' (I've seen this before).
'we hear' indicates a 'sounds like' (homophone) clue.
'break' is a homophone of 'BRAKE'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for brake that I've seen before include "Device for slowing vehicle" , "Slowing-down device" , "Thicket; estate car" , "Slower" , "Thicket; fern; slow down" .)