Lead sanctimonious bunch (5)
I believe the answer is:
pilot
'lead' is the definition.
(thesaurus)
'sanctimonious bunch' is the wordplay.
'sanctimonious' becomes 'pi'.
'bunch' becomes 'lot' ('lot' can be a synonym of 'bunch').
'pi'+'lot'='PILOT'
(Other definitions for pilot that I've seen before include "He steers ship or plane" , "Ship's guide" , "trial episode" , "Name of Mr Rochester's dog" , "One licensed to fly" .)