I agree with Abusaf. And I'd like to add that to look for this word in the dictionary look under د-ع-و (In Hans Wehr, there's an entry for مدع under دعو ).
Among the meanings of this word, there's "prosecuter", which I think best fits in this context : military prosecuter.
The word (مدع) is pronounced as مُدَّعٍ (Mudda-in) and is the active participle of form viii of the root دعو . Thus, مُدَّعٍ was originally مُدْتَعِوٌ (Mud-ta-iwun) on the pattern of مُفْتَعِلٌ (Muf-ta-ilun) but as you know weak letters (such as the Waw) tend to fall away quite often, and the Ta because of its proximity to the Dal gets transformed into a Dal and the one gets assimilated into the other to ease pronunciation. This accounts for the double Dal in مُدَّعٍ (Mudda-in).