ac ‧ cost /əˈkɒst $ əˈkɒːst, əˈkɑːst/ BrE AmE verb [transitive] written
[ Date: 1500-1600 ; Language: French ; Origin: accoster , from Latin costa 'rib, side' ]
to go towards someone you do not know and speak to them in an unpleasant or threatening way:
He was accosted by four youths and forced to give them all his money.