Meaning of the Sanskrit Word: trtiyam

  trtiyam—the third    SB 8.22.2, Adi 5.77, Madhya 20.251
  trtiyam—the third one    SB 1.3.8
  trtiyam—the third month    SB 4.8.74
  trtiyam—third    SB 6.18.7
  trtiyam—for the third step    SB 8.21.29
  trtiyam—and a third son    SB 9.24.1
  trtiyam—the third wife    SB 8.13.9

Can't find any compound Sanskrit words containing trtiyam.