From Longman Dictionary of Contemporary Englishset on somebody phrasal verb British English1 set somebody/something on somebodyATTACK to make people or animals attack someone The farmer threatened to set his dogs on us.2 if you are set on by people or animals, you are suddenly attacked by them A thirty-five-year-old man was set on by four youths last night.Grammar Set on is usually passive in this meaning.3 set somebody on/onto somebody to give someone information about a person who you think has done something wrong, because you want that person to be found and caught If I refuse, he’ll set the police onto me. → set→ See Verb table
