'Posse comitatus' definitions:

Definition of 'posse comitatus'

noun

A temporary police force [syn: posse, posse comitatus]

From: GCIDE

Posse comitatus \Pos"se com`i*ta"tus\ [L. posse to be able, to have power + LL. comitatus a county, from comes, comitis, a count. See County, and Power.] [1913 Webster]
1. (Law) The power of the county, or the citizens who may be summoned by the sheriff to assist the authorities in suppressing a riot, or executing any legal precept which is forcibly opposed. --Blackstone. [1913 Webster]
2. A collection of people; a throng; a rabble. [Colloq.] [1913 Webster]
Note: The word comitatus is often omitted, and posse alone used. "A whole posse of enthusiasts." --Carlyle. [1913 Webster]
As if the passion that rules were the sheriff of the place, and came off with all the posse. --Locke. [1913 Webster]