Word Origin & History
posse1645 (in Anglo-L. from 1314), shortening of posse comitatus "the force of the country" (1626, in Anglo-L. from 1285), from M.L. posse "body of men, power," from L. posse "have power, be able" + comitatus "of the country," gen. of L.L. word for "court palace." Modern slang meaning "small gang" is probably
from Western movies.