[ 'pɒsi ]
■ noun
1》 N. Amer. historical a body of men summoned by a sheriff to enforce the law.
2》 (also ~ comitatus ˌkɒmɪ'teɪtəs ) Brit. historical the body of men above the age of fifteen in a county, whom the sheriff could summon to repress a riot or for other purposes. [ comitatus from med. L., 'of the county'.]
3》 informal a group of people with a common characteristic, interest, or purpose.
Origin
C17: from med. L., lit. 'power', from L. ~ 'be able'.