The word "unknowably" is often used to describe something that cannot be understood or comprehended. However, there are several synonyms that can be used to convey a similar meaning. Words such as incomprehensibly, inscrutably, impenetrably, unfathomably, and inexplicably can all be used to describe something that is difficult or impossible to understand. Additionally, words such as mysterious, enigmatic, and cryptic can be used to convey a sense of intrigue or mystery surrounding a particular subject. Using these synonyms can help to add depth and nuance to your writing, as well as convey a more complex or nuanced meaning.