posse comitatus

noun2

1. •
   (figurative) Any band of men, especially armed or hostile.

   • With him retired his ‘posse comitatus,’ / The attorney last, who linger'd near the door / Reluctantly […] — 1819
2. •
   (historical) The able-bodied men over 15 in a given county who can be summoned by the sheriff to help keep the peace, or arrest a felon; also a group of men so gathered.

   • They are the standing army, and the militia, jailers, constables, posse comitatus, etc. — 1849