Adler classifies this entry as a 'sacred gloss'; see further n. 1 below.
The headword verb is the present indicative (and subjunctive) active, first person singular; see generally LSJ s.v., and cf. sigma 1235.
[1] The glossing verb (sigma 1420; cf. sigma 1418, sigma 1419) is the same grammatical form as the lemma. It is common in ecclesiastical contexts, where its connotation is I congregate, e.g. for a religious observance; note the cognate sunagwgh/, synagogue. The headword is identically glossed at ps.-Zonaras (Tittmann) 1681.3. Adler also cites Lexicon Ambrosianum 623.