Stopper I say ending in neck? (4)
I believe the answer is:
cork
'stopper' is the definition.
(I know that cork is a type of stopper)
'i say ending in neck?' is the wordplay.
'i say' becomes 'cor' (both are expressions of surprise).
'ending in' suggests the final letters.
The last letter of 'neck' is 'k'.
'cor'+'k'='CORK'
(Other definitions for cork that I've seen before include "Common bottle stopper" , "Tree bark from the South of Ireland?" , "Bark used for floats and stoppers" , "Irish city or county" , "Buoyant substance from a tree" .)