Doubt
Middle English: from Old French doute (noun), douter (verb), from Latin dubitare ‘hesitate’, from dubius ‘doubtful’ (see dubious).
wiktionary
The verb is derived from Middle English douten(“to be in doubt, feel unsure; to be afraid or worried; to hesitate; to be confused; to have respect or reverence”)[and other forms], [1] from Old French douter, doter, duter (compare Middle French doubter), from Latin dubitāre(“to hesitate”), the present active infinitive of dubitō(“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”)). Although the Middle English form of the word was spelled without a b, this letter was later introduced through the influence of the Latin words dubitāre and dubitō. However, the English word continued to be pronounced without the b sound. [2]
The noun is derived from Middle English dout, doute(“uncertain feeling; questionable point; hesitation; anxiety, fear; reverence, respect; something to be feared, danger;”)[and other forms], [3] from Old French doute, dote, dute(“uncertain feeling, doubt”), from doter, douter, duter(“to doubt; to be afraid of, fear”) (compare Middle French doubter; modern French douter(“to doubt; to suspect”)); see further etymology above. [4]
Displaced Old English twēo(“doubt”) and twēoġan(“to doubt”).
etymonline
doubt (v.)
c. 1200, douten, duten, "to dread, fear, be afraid" (a sense now obsolete), from Old French doter "doubt, be doubtful; be afraid," from Latin dubitare "to doubt, question, hesitate, waver in opinion" (related to dubius "uncertain"), from duo "two" (from PIE root *dwo- "two"), with a sense of "of two minds, undecided between two things." Compare dubious. Etymologically, "to have to choose between two things."
The sense of "fear" developed in Old French and was passed on to English. Meaning "to be uncertain, hesitate or waver in opinion" is attested in English from c. 1300. The transitive senses of "be uncertain as to the truth or fact of" and "distrust, be uncertain with regard to" are from c. 1300.
The -b- was restored 14c.-16c. in French and English by scribes in imitation of Latin. French dropped it again in 17c., but English has retained it.
It replaced Old English tweogan (noun twynung), from tweon "two," on notion of "of two minds" or the choice between two implied in Latin dubitare. Compare German Zweifel "doubt," from zwei "two."
doubt (n.)
c. 1200, doute, "uncertainty with regard to the truth of something," from Old French dote (11c.) "fear, dread; doubt," from doter (see doubt (v.)). The -b- was inserted later, as in the verb. Meaning "a matter of uncertainty" is from late 14c. Phrase no doubt "without question, certainly" is from c. 1400.
