The headwords are aorist middle subjunctive -- first person singular and first person plural -- of eu(ri/skw (epsilon 3697); and the point being made is that such subjunctives are sometimes found where we would expect the future indicative ("prospective subjunctive").
The primary headword eu(/rwmai occurs in Pausanias and Gregory of Nazianzus, but both times with normal subjunctive usage.
[1] Likewise, according to Adler, in the Ambrosian Lexicon (2660).
[2] Likewise in ps.-Herodian (274)