Question

Sometimes spelling reform works in reverse, making spelling less phonetic. The words doubt and debt were borrowed from French as douse and det (or dette), but a new awareness of their Latin origins led scholars to insert a b in each to reflect their etymologies.
Look up both words in your dictionary.

What is the proper Latin root of doubt?

douten
douter
dubitare

Answer 1

Dubitāre is the answer

Answer 2

The answer is: dubitāre .

Dubitāre in Latin means to doubt, question, hesitate or waver in opinion.  

Considering the rest of the alternatives, douten comes from Old French and signifies to dread, fear or be afraid. It is an obsolete word nowadays. As regards douter, it is a French transitive verb that means to hesitate or to doubt.