Morass was developed by politician (5)
I believe the answer is:
swamp
'morass' is the definition.
(thesaurus)
'was developed by politician' is the wordplay.
'developed' is an anagram indicator.
'by' means one lot of letters go next to another.
'politician' becomes 'MP' (Member of Parliament).
'was' is an anagram of 'swa'.
'swa'+'mp'='SWAMP'
(Other definitions for swamp that I've seen before include "Engulf" , "marshy tract" , "Marshy land" , "Boggy area" , "In flood" .)