[L. posse to be able, to have power + LL. comitatus a county, from comes, comitis, a count. See County, and Power.]

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.

2. A collection of people; a throng; a rabble. [Colloq.]

Note: The word comitatus is often omitted, and posse alone used. «A whole posse of enthusiasts.» Carlyle.

As if the passion that rules were the sheriff of the place, and came off with all the posse.

Webster 1913 Dictionary edited by Patrick J. Cassidy