Right to stop crush in Slough (5)
I believe the answer is:
marsh
'slough' is the definition.
(thesaurus)
'right to stop crush' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to stop' indicates putting letters inside.
'crush' becomes 'mash' ('mash' can be a synonym of 'crush').
'r' put into 'mash' is 'MARSH'.
'in' is the link.
(Other definitions for marsh that I've seen before include "Bog, swamp" , "eg Romney" , "Swampland" , "Swampy ground" , "Fen" .)