Both headword and gloss are genitive singulars.
Same entry in other lexica: Photius, Lexicon delta807 (with, however, the faulty headword dusea/ktou, obelized by Theodoridis), Hesychius delta2547, Lexica Segueriana delta202.25.
The lemma stems from a biblical passage, 3 Maccabees 6.31 LXX (pikrou= kai\ dusaia/ktou mo/rou), the only independent occurrence of the adjective.
[1] On this gloss, an adjective taken from tragedy, see the full note at delta 1605.