Believably is an adverb that describes something that is able to be believed or accepted. If something is not believable, then it is considered to be unbelievable or incredulous. Alternatively, if something is questionable or unreliable, it can be described as unconvincing or implausible. On the other hand, if something is overly convincing or persuasive, it may be described as exaggerated or unrealistic. Ultimately, the opposite of believably depends on the context and how it is being used. However, some common antonyms for believably include unbelievably, doubtfully, improbably, and implausibly.