Unperceptively is a word that means "without being noticed or detected." However, there are many synonyms that can be used in its place depending on the context of the sentence or phrase. Some examples include inconspicuously, stealthily, silently, surreptitiously, quietly, imperceptibly, and indiscernibly. These words can be used to describe actions taken without being noticed, movements made in secret, or thoughts or feelings hidden from others. Choosing the right synonym can help convey the intended meaning of a sentence or passage, and add depth and nuance to a piece of writing.