/ ˈpɒsi; NAmE ˈpɑːsi/ noun
1.
( informal ) a group of people who are similar in some way, or who spend time together :
a little posse of helpers
2.
(in the US in the past) a group of people who were brought together by a sheriff (= an officer of the law) in order to help him catch a criminal
3.
( informal ) a group of young men involved in crime connected with drugs
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WORD ORIGIN
mid 17th cent.: from medieval Latin , literally power , from Latin posse be able.