A temporary police force WordNet 3.0 & Open English WordNet

The posse comitatus, frequently shortened to posse, is in common law a group of people mobilized by the conservator of peace – typically a reeve, sheriff, chief, or another special/regional designee like an officer of the peace potentially accompanied by or with the direction of a justice or ajudged parajudicial process given the imminence of actual damage – to suppress lawlessness, defend the people, or otherwise protect the place, property, and public welfare Wikipedia

Authority of a law officer to conscript any able-bodied males to assist him. Wikipedia Disambiguation

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. Wiktionary