- 1completely unreasonable, especially in a way that is shocking or annoying synonym outrageous These claims are absolutely preposterous! It's preposterous to suggest that everything was her fault!
- 2unusual in a silly or shocking way synonym outrageous The band members were famous for their preposterous clothes and haircuts.
adverb a preposterously expensive bottle of wineSee preposterous in the Oxford Advanced Learner's Dictionary
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