By coincidence is a phrase used to describe an event or outcome that occurs unintentionally. However, there are several other ways to convey the same meaning. Some synonyms for by coincidence include by chance, accidentally, unplanned, fortuitously, coincidentally, incidentally, and happenstantially. These words could be used in place of by coincidence to describe something that occurred without any prior planning or design. Whether you use by chance or coincidentally, the meaning remains the same. It is important to note that the context in which these words are used can influence the message that is conveyed.