An opaque entry, and made the more so because it appears in other lexica in different forms. In Photius (alpha231 Theodoridis) the lemma itself is the adjective only, i.e. di/khn is lacking; the Synagoge (alpha82) has di/khn as the first part of the gloss. All that seems certain, therefore, is that a)gorai/an (accusative singular) is quoted from somewhere.
The glossing term dikaiologia can mean either a defense plea or a forensic speech of any kind: see LSJ s.v.