[1] The headword as transmitted is second person singular, perfect active, of a)sunqete/w. Very similar glossing in other lexica, e.g. Photius eta282, where however the opening word of the gloss is not the relative pronoun a(/ but h)/, i.e. apparently proffering the glossing verbs as synonyms of the headword. Theodoridis accordingly obelizes h)sunqe/thkas and regards it as a mis-transmission of the phrase h)\ sunte/qeikas; cf. generally Hesychius sigma2712.
[2] Theodoret (PG 80.1448c) on Psalm 72.15 LXX (which actually has first person singular).