英语词源字典 - 在线词源网站

dubious (adj.)[dubious 词源字典]: 1540s, from Latin dubiosus "doubtful," from dubium "doubt," neuter of dubius "vacillating, moving two ways, fluctuating;" figuratively "wavering in opinion, doubting, doubtful," from duo "two" (see two), with a sense of "of two minds, undecided between two things." Old English also used tweo "two" to mean "doubt." Compare doubt (v.). Related: Dubiously; dubiousness.[dubious etymology, dubious origin, 英语词源]
vacillate (v.): 1590s, "to sway unsteadily," from Latin vacillatus, past participle of vacillare "sway to and fro; hesitate" (see vacillation). Meaning "to waver between two opinions or courses" is recorded from 1620s. Related: Vacillated; vacillates; vacillating.
vague (adj.): "uncertain as to specifics," 1540s, from Middle French vague "empty, vacant; wild, uncultivated; wandering" (13c.), from Latin vagus "strolling, wandering, rambling," figuratively "vacillating, uncertain," of unknown origin. Related: Vagueness.
wishy-washy (adj.): 1690s, "feeble or poor in quality," reduplication of washy "thin, watery." Meaning "vacillating" first recorded 1873.