When it comes to expressing uncertainty or doubt about something, there are a multitude of synonyms that can be used instead of "open to question." Some alternatives include "doubtful," "unsettled," "unclear," "ambiguous," "equivocal," "controversial," and "debatable." These words can be used to convey the idea that there is room for discussion or disagreement about a particular topic or statement. For example, "the accuracy of the data is in doubt," or "the validity of the theory is uncertain." By utilizing these synonyms, writers and speakers can add nuance and precision to their language and avoid repetition.