The affix ap comes after the verb aj 'to go' when the preposition sam and ut are in composition and the word so formed refers to beasts.,
This debars घञ्. The root अज 'means to go, to throw'. When preceded by सम्, it means 'a collection'; and preceded by उत् it means 'driving'. As समजः पशूनां 'a herd of cattle'; उदजः पशूनां 'driving forth of cattle'.
Why do we say 'when applying to cattle'? Observe समाजो ब्राह्मणानां, उदाजः क्षत्रियाणां ।,