The headword is a masculine noun in the nominative singular; cf. generally sigma 405, epsiloniota 25 (gloss), LSJ s.v., and, with a more common sense, this word already at sigma 406. The source of the entry is unidentifiable. With the meaning apparently given in the gloss, the headword appears only in lexicography; but see next note.
[1] Identical glossing in the Synagoge (sigma78) Photius' Lexicon (sigma208 Theodoridis), and likewise already Hesychius sigma630, who adds h)\ o( a)hdh/s. The gloss o( mikro\s si=tos is hard to comprehend as it stands; there is great attraction in the suggested emendation -- by Salmasius (Claude Saumaise, 1588-1653) and Coraes -- to mikro/sitos, he who eats little; cf. LSJ.