Momentous, an adjective that describes something that is significant or important, can be replaced by various synonyms. One of the most commonly used synonyms for momentous is significant. Something that is significant has great importance or impact. Another word that can be used synonymously with momentous is crucial. This describes something that is crucially important or essential. Monumental is another word that means something that is important and impressive due to its size or scale. Other synonyms for momentous include consequential, historic, and pivotal, all of which describe something that holds great significance or impact. In conclusion, the English language is full of rich vocabulary, and it's always a good idea to use synonyms to make your writing more dynamic and interesting.