What is "tuisto"

According to Tacitus's Germania (98 CE), "In their ancient songs, their only form of recorded history, the Germans celebrate the earth-born god, Tuisto. They assign to him a son, Mannus, the author of their race, and to Mannus three sons,..." The figure remains the subject of some scholarly discussion, largely focused upon etymological connections and comparisons to figures in later (particularly Norse) Germanic mythology. In the larger Indo-European pantheon, Tuisto is equated to the Vedic Tvastar.