posseyoudaoicibaDictYouDict[posse 词源字典]
posse: [17] Posse was the Latin verb for ‘be able’. It was a conflation of an earlier expression potis esse ‘be able’; and potis ‘able’ was descended from an Indo-European base *potthat also produced Sanskrit pati- ‘master, husband’ and Lithuanian patis ‘husband’. In medieval Latin posse came to be used as a noun meaning ‘power, force’.

It formed the basis of the expression posse comitātus, literally ‘force of the county’, denoting a body of men whom the sheriff of a county was empowered to raise for such purposes as suppressing a riot. The abbreviated form posse emerged at the end of the 17th century, but really came into its own in 18th- and 19th-century America.
=> possible, potent[posse etymology, posse origin, 英语词源]
posse (n.)youdaoicibaDictYouDict
1640s (in Anglo-Latin from early 14c.), shortening of posse comitatus "the force of the county" (1620s, in Anglo-Latin from late 13c.), from Medieval Latin posse "body of men, power," from Latin posse "have power, be able" (see potent) + comitatus "of the county," genitive of Late Latin word for "court palace" (see comitatus). Modern slang meaning "small gang" is probably from Western movies.