Both headword (ignored in LSJ) and gloss are unattested outside lexicography, where they appear together (the latter with the variant dusgnwmo/nwn, a hapax legomenon, in Photius, Lexicon delta810).
Adrados’ Diccionario (see bibliography below) s.v., quoting this entry, considers duse/ktwn the genitive plural of duse/kths. But more probably, given the glossing (and the affinity of dusgnw/mwn with a)gnw/mwn), it is nominative singular; if so, headword and gloss alike are nasal forms of the third declension.
The etymology of duse/ktwn itself may derive from the combination of dus- with e)/xw (cf. the verbal adjective e)kte/os), 'I have/hold', here figuratively 'I hold mentally, 'I understand'.