For every one inside wharf (4)
I believe the answer is:
pier
'wharf' is the definition.
(thesaurus)
'for every one inside' is the wordplay.
'for every' becomes 'per' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'inside' is an insertion indicator.
'per' enclosing 'i' is 'PIER'.
(Other definitions for pier that I've seen before include "Break-water or landing stage" , "Wharf or pillar" , "Promenade over water" , "Seaside attraction" , "Structure with a deck, built over water" .)