Both the headword (which must be quoted from somewhere) and the glossing phrase are in the neuter nominative/accusative singular.
The entry = Synagoge delta395 (Lexica Segueriana 202.24) and Photius, Lexicon delta806.
We can consider this adjective, in both -feukt and -fukt forms (according to LSJ, and see web address 1 below), an exclusively Patristic and Byzantine term. It occurs indeed mostly in Cyril of Alexandria and it is first attested in John Chrysostom and in Eusebius, Commentary to Psalms 23.1229 (later quoted by Cyril, Expositio in Psalmos 69.1248).
[1] The gloss seems to be strongly Cyrillian, since even Hesychius delta2548, identical to the present entry, is considered by Latte a Cyrillian interpolation -- because, as he argues, we find it in family v, g and S of the Cyrillian Lexicon manuscripts (see Latte's Prolegomena). The complete absence of this term from classical writers and its extensive presence in Cyril's works lend weight to this opinion.