Influence of one million crowd (7)
I believe the answer is:
impress
'influence' is the definition.
(thesaurus)
'of one million crowd' is the wordplay.
'of one' becomes 'i' (I've seen this in other clues).
'million' becomes 'm' (abbreviation).
'crowd' becomes 'press' (press is a kind of crowd).
'i'+'m'+'press'='IMPRESS'
(Other definitions for impress that I've seen before include "strike" , "Cut a dash" , "Simpers to affect favourably" , "Produce a strong, lasting impression on" , "Make a lasting effect (on)" .)