Adumbral is an adjective that describes something as being shadowy or indistinct. Some antonyms for this word include bright, clear, distinct, and illuminated, all of which describe something that is well-defined and visible. If something is adumbral, it's also possible to describe it as vague, nebulous, uncertain, or obscure. Its opposite, on the other hand, would be something that is certain or clearly defined. For instance, the antonym for adumbral might be used to describe a bright and sunny day, a clear and concise argument or a well-defined goal. Antonyms are an effective tool for helping to add contrast to our language and make our writing more specific and engaging.