The headword, nominative plural is this masculine noun, is attested as such only in lexicography (see below), but is a homophonous late Greek spelling of a word which was normally spelled with an iota in the first syllable in the classical period (siroi/). The only literary attestations of this latter form are in Sophocles fr. 276 Radt (from his lost Inachus) and Artemidorus 2.24.
[1] = Synagoge sigma43, Photius sigma123 Theodoridis; cf. Hesychius sigma347. Attestations of this meaning for the headword are difficult to find; Herodian, On Orthography 3.2.448.23, and Pollux 9.49 are ambiguous. Theodoridis on Photius believes that Nauck (Philologus 6 (1851): 417.2) was possibly correct in suggesting that this gloss properly belongs to the headword shkoi/ (cf. sigma 303).
[2] For this sense see generally LSJ s.v. siro/s, I (citing inter alia an Athenian inscription of the fifth century BCE), and cf. Hesychius sigma724 s.v. siroi=s (dative plural) = Synagoge sigma89, Photius sigma236; Hesychius sigma727 s.v. sirou=s (accusative plural).