PM was jostled in Slough (5)
I believe the answer is:
swamp
'slough' is the definition.
(I've seen this before)
'pm was jostled' is the wordplay.
'jostled' indicates anagramming the letters (I've seen this in other clues).
'pm'+'was'='pmwas'
'pmwas' is an anagram of 'SWAMP'.
'in' acts as a link.
(Other definitions for swamp that I've seen before include "Waterlogged ground" , "Engulf" , "Slough" , "Bog, marsh" , "Boggy area" .)