The headword is the neuter nominative/accusative singular of the two-ending adjective pollosthmo/rios (a number of times smaller: LSJ s.v.). Here however, and presumably therefore in the context from which it was quoted (perhaps Lucian, Icaromenippus 18), it simply means a (sc. small) geographical fraction, i.e. as if it were the phrase pollosto\n mo/rion; cf. e.g. Thucydides 6.86.5 with scholion, and generally LSJ s.v. pollosto/s, 3.