The headword is the present active infinitive of the contract verb sitometre/w, I deal out portions of grain. It is perhaps extracted here from the Polybius passage quoted below; see in any event LSJ s.v., showing (inter alia) that its earliest surviving attestations are in that author.
[1] The glossing verb form is the present infinitive active of pare/xw, I hand over, furnish, provide, supply; see generally LSJ s.v.
[2] This neuter noun (sito/metron in ms A) occurs most famously in the New Testament (Luke 12.42), in connection with the parable of the sower.
[3] Polybius fr. 75 Büttner-Wobst (unplaced).
[4] An approximation of Xenophon, Cyropaedia 1.6.36 (web address 1); see de Boor, p. 35.
[5] See generally LSJ s.v.; instances in Demosthenes and elsewhere.