Part of speech: Noun
uncertainty about the truth or factuality or existence of something
Example: the dubiousness of his claim; there is no question about the validity of the enterprise
Part of speech: Noun
the state of being unsure of something
Part of speech: Verb
consider unlikely or have doubts about
Example: I doubt that she will accept his proposal of marriage
Part of speech: Verb
lack confidence in or have doubts about
Example: I doubt these reports; I suspect her true motives; she distrusts her stepmother