Meaning of the Sanskrit Word: mantrabhyam

  mantrabhyam—with the two mantras (om namo bhagavate vasudevaya and om namo narayanaya)    SB 6.8.4, SB 6.8.5, SB 6.8.6, SB 6.8.4-6

Can't find any compound Sanskrit words containing mantrabhyam.