The headword is genitive singular of the adjective ei)dh/mwn, evidently quoted from somewhere. Compare generally Hesychius epsilon747, nominative with the gloss gnwstiko/s (and the adverbial form at epsilon762, with the gloss e)pisthmo/nws); and see also epsilon 2613. As a gloss, the adjective occurs in Hesychius delta36 and delta465.
cf. generally epsiloniota 30.