Adjective: imperceptible ,im-pu(r)'sep-tu-bul
- Impossible or difficult to perceive by the mind or senses
"an imperceptible drop in temperature";
- unperceivable
See also: impalpable, inaudible, incognisable [Brit], incognizable, incognoscible, indiscernible, insensible, invisible, subliminal, undetectable, unhearable, unobservable, unseeable
Antonym: perceptible
Encyclopedia: Imperceptible