When it comes to expressing a situation that's exceptionally serious, the phrase "very grave" is commonly used. However, there are several synonyms that can be used to convey a similar meaning. One such synonym is "dreadful", which emphasizes the severity of a situation by suggesting that it's highly alarming and possibly catastrophic. Another option is "severe", which suggests that something is not only very serious, but also potentially damaging or harmful. Additionally, the phrase "extremely concerning" or "highly worrisome" can be used to describe a situation that's very grave, as it conveys a sense of urgency and anxiety. Ultimately, the choice of synonym depends on the context and the desired emphasis.