Same entry in the Synagoge, Photius (mu342 Theodoridis), and the Anecdota graeca (ed. L. Bachmann) 299.27. The headword is the third person singular of the pluperfect indicative active of metalagxa/nw (mu 698, mu 781, cf. mu 699); cf. its use at mu 591. It must be quoted from somewhere -- perhaps Agathias, Histories 4.21.3.
I take the appearance of meth/|ei as an apparently mistaken definition of metalagxa/nei at mu 699 (cf. mu 786) to be a copying error for a form of the verb found in the gloss here, perhaps mete/xei.
[1] cf. mu 698.