1909 in the figurative sense of "complete overthrow" of something; from German Götterdämmerung (18c.), literally "twilight of the gods," from genitive plural of Gott "god" (see god) + Dämmerung "dusk, twilight," from PIE root *teme- "dark" (see temerity). Used by Wagner as the title of the last opera in the Ring cycle. It translates Old Norse ragna rok "the doom or destruction of the gods, the last day, world's end." A better transliteration is Goetterdaemmerung.
"doubtfulness, dubiousness," 1650s, from Late Latin dubietas "doubt, uncertainty," from Latin dubius "vacillating, fluctuating," figuratively "wavering in opinion, doubting" (see dubious). Earlier in the same sense were dubiosity (1640s), dubiousness (1650s); also see dubitation.
Ignorance is the mother of two filthy daughters; the first daughter of Ignorance is called dubiety, or doubtfulnesse, which is a continual wavering in opinion; a knowing man hath a fixt spirit, and settled judgement, but an ignorant man is a double-minded man, though he be never so resolute and wilful in his opinions. [W. Geering, "The Mischiefes and Danger of the Sin of Ignorance," London, 1659]