Imperceptible a. : Not perceptible; not to be apprehended or cognized by the souses; not discernible by the mind; not easily apprehended.

Example:
How do we perceive the seemingly Imperceptible?

Taxonomy
Merriam-Webster Online Dictionary, Dictionary, webster, cep, Word Games, Webster Online Dictionary with audio pronunciations, Middle English, thesaurus, Medieval Latin, Late Latin, glossary, language, ESL, ble, adjective, Etymology, Middle French, Latin.

Defination from the web:
imperceptible from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... not perceptible by a sense or by the mind : extremely slight, gradual, or subtle <imperceptible differences> — im·per·cep·ti·bly -ˈsep-tə-blē adverb ...