Forgettingly is an infrequently used word that means "in a forgetful manner." However, it can be substituted with a few other words that may be more commonly used. These include absentmindedly, inadvertently, negligently, and unintentionally. These words convey the same idea of forgetting something or not paying attention to it adequately. Synonyms can be helpful in writing to avoid repetition of the same word, but it is also important to use them appropriately to ensure that the meaning remains consistent. In any case, whether you use forgettingly or one of its synonyms, ensure that your message is clear and that your tone is appropriate for your audience.