doubt
noun
the state of being unsure of something
uncertainty about the truth or factuality or existence of something
“the dubiousness of his claim”
“there is no question about the validity of the enterprise”
verb
consider unlikely or have doubts about
“I doubt that she will accept his proposal of marriage”
lack confidence in or have doubts about
“I doubt these reports”
“I suspect her true motives”
Source: WordNet 3.1, Princeton University