Place is somewhat foul, i.e. unpleasant (4)
I believe the answer is:
lieu
'place' is the definition.
(as in the phrase 'in lieu of')
'somewhat foul i e unpleasant' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'LIEU' is hidden in the letters of 'foul i e unpleasant'.
'is' acts as a link.
(Other definitions for lieu that I've seen before include "In ... of; in exchange for" , "'In ..., instead (4)'" , "Stead - place" , "In - of means instead of" , "Place - position" .)