From Longman Dictionary of Contemporary Englishpossepos‧se /ˈpɒsi $ ˈpɑːsi/ noun [countable] 1 informalGROUP OF PEOPLE a group of the same kind of peopleposse of I was surrounded by a posse of photographers.2 SCa group of men gathered together by a sheriff (=local law officer) in the US in past times to help catch a criminal3 American English informalFRIENDLY a) someone’s group of friends – used especially by young people b) a group of friends from a particular place who share an interest in rap, hip-hop, or house music SYN massive British English
Examples from the Corpus
posse• At any rate, the males leave their parties and come together in a posse.• An ex-Texas Ranger named Harry Love organized a posse that scoured the state.• No more talk about posses, no more pickups and runs.• This Tank Girl-style posse is only seven months old, but already it has grown beyond the founders' wildest dreams.• But after the bandits' escape through the chimney, the posse eventually tracked them down.• You don't share with strangers, so prices get progressively cheaper the more there are in your posse.Origin posse (1600-1700) Medieval Latin posse comitatus “power of the county” 