Tar makes snake stop (7)
I believe the answer is:
asphalt
'tar' is the definition.
(synonyms)
'snake stop' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'stop' becomes 'halt' (halt can mean to stop).
'asp'+'halt'='ASPHALT'
'makes' acts as a link.
(Other definitions for asphalt that I've seen before include "Mixture of tar and gravel used in road surfaces" , "Pitch surface" , "Paving material" , "Road-buiding material" , "Road-building material" .)