Redevelopment of seacoast involving one couple (9)
I believe the answer is:
associate
'couple' is the definition.
(thesaurus)
'redevelopment of seacoast involving one' is the wordplay.
'redevelopment of' indicates an anagram (I've seen 'redevelopment' mean this (I've seen this in other clues)).
'involving' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'seacoast' is an anagram of 'assocate'.
'assocate' going around 'i' is 'ASSOCIATE'.
(Other definitions for associate that I've seen before include "Make a logical or casual connection" , "friend?" , "Person one works or spends time with" , "Link" , "Get together with" .)