doubt 
(dout)
(dout)v. doubt·ed, doubt·ing, doubts
v.tr.
1. To be undecided or skeptical about: began to doubt some accepted doctrines.
2. To tend to disbelieve; distrust: doubts politicians when they make sweeping statements.
3. To regard as unlikely: I doubt that we'll arrive on time.
4. Archaic To suspect; fear.
v.intr.
To be undecided or skeptical.
n.
Idioms: 1.
a. The state of being uncertain about the truth or reliability of something. See Synonyms at uncertainty.
b. often doubts A feeling of uncertainty or distrust: had doubts about his ability.
2. A point about which one is uncertain or skeptical: reassured me by answering my doubts.
3. The condition of being unsettled or unresolved: an outcome still in doubt.
beyond/without doubt
Without question; certainly; definitely.
no doubt
1. Certainly.
2. Probably.
[Middle English douten, from Old French douter, from Latin dubitāre, to waver; see dwo- in the Appendix of Indo-European roots.]
doubter n.
Usage Note: The choice of what conjunction to use following doubt and doubtful is a perennial usage problem. When doubt and doubtful indicate strong uncertainty, the Usage Panel prefers whether and that over if. In our 2008 survey, 51 percent indicated that they would use that, while 43 percent preferred whether in the following sentence: At one time it was doubtful [that/whether/if] the company could recover from its financial difficulties, but the government loan seems to have helped. Only 6 percent said they would favor if in this sentence, probably because if has a more informal tone. When the expectation for the outcome is negative, that tends to be used. Some 86 percent of the Panel prefer that in the sentence I doubt [that/whether/if] it will rain tomorrow (where the expectation is that it probably won't rain), with whether getting the preference of only 6 percent and if getting 7 percent. Note that, in certain kinds of sentences, the choice of conjunction can carry subtle differences in implication. That is the best choice when the truth of the clause following doubt is assumed, as in negative sentences and questions. Thus I never doubted for a minute that I would be rescued implies "I was certain that I would be rescued." By the same token, Do you doubt that you will be paid? may be understood as a rhetorical question meaning "Surely you believe that you will be paid," whereas Do you doubt whether you will be paid? expresses a genuine request for information (and might be followed by Because if you do, you should make the client post a bond). Note that it is also acceptable to omit that in these sentences: I doubt she will accept the nomination. In other cases, however, this distinction between whether and that is not always observed. · When doubt is negated to indicate belief or certainty, the clause following doubt is sometimes introduced with but that or simply but, as in I do not doubt but that they will come. This construction has been used by many fine writers, but some critics object to its use in formal writing. Dropping the but easily solves this problem. See Usage Notes at but, if.