Dubious /d(y)o͞obēəs/ adj. 

Definition: The word dubious has two separate meanings. First, it means when someone is unsettled in their opinion. Second, dubious refers to something giving rise to uncertainty. In particular, it refers to occasions when you are not sure about the outcome or quality of a situation or item. In general, dubious tends to refer to a feeling of mistrust or suspicion. Because it has several meanings, you must make sure that if you are using a synonym that it makes sense in your particular case.

Etymology: Dubious comes from the Latin verb dubare, which means hesitating in the choice of multiple options or choices. It is also related to the Latin duo meaning two. The word was first used in the mid-1500s, referring to the secondary meaning of causing uncertainty in a situation.

In a Sentence

She was not sure she wanted to proceed with the dubious plan.

He was given the dubious honor of making sure the children got to bed on time.

She was not completely convinced of the dubious results of the study once she learned how the experiment was performed.

Synonyms 

Doubtful, Questionable, Suspicious

Antonyms 

Indisputable, Certain, Hands-Down