The word "most fuliginous" refers to something that is extremely dark, murky, or sooty. Some antonyms for this word are light, ethereal, and clear. Light suggests brightness or illumination, while ethereal implies a light, airy quality that is otherworldly. Clear, on the other hand, suggests transparency, lucidity, or a lack of obscurity. These three words are the opposite of "most fuliginous" as they connote qualities that are opposite to darkness, murkiness, or sootiness. Depending on the context, these terms can be used to contrast with "most fuliginous" or to emphasize its negative qualities.