Dubious
mid 16th century (in dubious (sense 2)): from Latin dubiosus, from dubium ‘a doubt’, neuter of dubius ‘doubtful’.
wiktionary
From Latin dubius; like doubt, from Latin duo (cognate to English two), implying “two alternatives” (yes or no, true or false, etc.).
etymonline
dubious (adj.)
1540s, "puzzling, occasioning doubt or uncertainty;" 1630s, "doubtful, hesitating in opinion;" from Late Latin dubiosus "doubtful," from Latin dubium "doubt," neuter of dubius "vacillating, moving two ways, fluctuating;" figuratively "wavering in opinion, doubting, doubtful," from duo "two" (from PIE root *dwo- "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.
