doubt

Etymology tree Latin dubō Proto-Indo-European *-h₂ Proto-Indo-European *-éh₂ Proto-Indo-European *-yéti Proto-Indo-European *-eh₂yéti Proto-Italic *-āō Latin -ō Latin -tō Latin -itō Latin dubitō Old French doterbor. Middle English douten ▲ Old French doter Old French doutebor. Middle English doute ▲ English dubiousinflu. ▲ Latin dubitōinflu. English doubt The verb is derived from Middle English douten (“to doubt, fear, worry”) [and other forms], from Old French douter, doter, duter (compare Middle French doubter), from Latin dubitāre (“to be uncertain, doubt; to hesitate, waver in coming to an opinion; to consider, ponder”); the further etymology is uncertain, but one theory is that dubitō may be derived from dubius (“fluctuating, wavering; doubtful, dubious, uncertain”), from duhibius (“held as two”), from duo (“two”) (ultimately from Proto-Indo-European *dwóh₁ (“two”)) + habeō (“to have, hold”) (possibly ultimately from Proto-Indo-European *gʰeh₁bʰ- (“to grab, take”)). Spelling reformers of the early modern period added the letter b to reflect the Latin root dubitō, but it has never been pronounced in English. The noun is derived from Middle English dout, doute (“uncertainty, hesitation; questionable point; anxiety, fear, reverence”) [and other forms], from Old French doute, dote, dute (“uncertain feeling, doubt”), from doter, douter, duter (“to doubt, fear”) (compare Middle French doubter; modern French douter (“to doubt, suspect”)); see further etymology above. Displaced Old English twēo (“doubt”) and twēoġan (“to doubt”).

来源：wiktionary