Headword and gloss are different forms of the same verbal form; cf. eta 80, eta 82.
The headword verb is a poorly attested form (in literature only in Lucian) of the second person singular, pluperfect, of οἶδα , “I know”; and according to Aelius Herodianus, Περὶ ὀρθογραφίας 3.2.517, this form, and the more common one, ᾔδησθα , derive from ᾔδεις (= the present gloss) by ἐπέκτασις , “extension”, of the θα syllable. According to Smyth, section 798, this form occurs in the best manuscripts of Plato and elsewhere, but is less correct Attic [than ᾔδησθα ] (web address 1).
The Lexicon Ambrosianum (Ambrosianus B12 sup. fol. 77r) has a similar entry to this one, but with better spelling: ᾔδησθα: ᾔδεις: κατὰ ἐπέκτασιν τῆς Θα , “you knew: you knew, by extension of the θα [syllable]” (note the quotation from Aelius Herodianus). With the same headword as in the Lexicon Ambrosianum, glossed by ᾔδεις (as here), we have Hesychius, Lexicon eta120, probably interpolated – according to K.Latte - by the family S or N of Glossarium Cyrilli. However, Glossarium Cyrilli, Coislinianus 394 fol. 113r has an entry identical to this one.