Singleness of purpose as oily dirt is shifted (10)
I believe the answer is:
solidarity
'singleness of purpose' is the definition.
(thesaurus)
'as oily dirt is shifted' is the wordplay.
'is shifted' is an anagram indicator.
'as'+'oily'+'dirt'='asoilydirt'
'asoilydirt' is an anagram of 'SOLIDARITY'.
(Other definitions for solidarity that I've seen before include "Unity" , "Showing oneness" , "Mutual support within a group" , "Esprit de corps" , "Supposed alien pattern in corn" .)