There are a variety of words that can be used as synonyms for "undet," which typically means undetected or unnoticed. Some possible alternatives include unseen, unobserved, unnoticed, hidden, concealed, imperceptible, overlooked, and invisible. Depending on the context in which it is being used, other synonyms might include unremarked, unrecorded, unregistered, or unacknowledged. Ultimately, the right synonym will depend on the precise meaning that is being conveyed and the tone that the writer or speaker wants to use. By choosing the right synonym, it is possible to make language more vivid and engaging, while also ensuring that the intended meaning is clear.