Rank smell obviously repels them at first (4)
I believe the answer is:
sort
'rank' is the definition.
(thesaurus)
'smell obviously repels them at first' is the wordplay.
'at first' says to take the initial letters.
The initial letters of 'smell obviously repels them' is 'SORT'.
(Other definitions for sort that I've seen before include "choice of characters frequently used in statistics" , "Arrange systematically" , "Type - arrange in groups" , "Separate - kind" , "Arrange in order" .)