Meaning of the Sanskrit Word: mahatalam

  mahatalam—Mahatala    SB 5.24.7
  mahatalam—the planet named Mahatala    SB 2.1.26
  mahatalam—the fifth planetary system below    SB 2.5.40, SB 2.5.41, SB 2.5.40-41

Can't find any compound Sanskrit words containing mahatalam.