Adventitiously is an adverb that means "by chance or accident." There are a number of synonyms for this word, including fortuitously, inadvertently, accidentally, coincidentally, unexpectedly, and by happenstance. These words all convey the same idea, that something happens without intentional planning or forethought. Depending on the context in which the word is being used, some synonyms may be more appropriate than others. It is important to choose the right synonym to convey the precise meaning intended and to ensure effective communication. Overall, there are many alternatives to the word "adventitiously" that can be used to add variety and depth to written or spoken language.