posse comitatus

[pos-ee kom-i-tah-tuh s, -tey-] /ˈpɒs i ˌkɒm ɪˈtɑ təs, -ˈteɪ-/
noun
1.
the body of persons that a peace officer of a county is empowered to call upon for assistance in preserving the peace, making arrests, and serving writs.
2.
a body of persons so called into service.
Origin
1620-30; < Medieval Latin: posse of the county
British Dictionary definitions for posse comitatus

posse comitatus

/ˌkɒmɪˈtɑːtəs/
noun
1.
the formal legal term for posse (sense 1)
Word Origin
Medieval Latin: strength (manpower) of the county
Encyclopedia Article for posse comitatus

ancient English institution consisting of the shire's force of able-bodied private citizens summoned to assist in maintaining public order. Originally raised and commanded by the sheriff, the posse comitatus became a purely civil instrument as the office of sheriff later lost its military functions. From time to time, legislation gave authority to other peace officers and magistrates to call upon the power of the county.

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