imperceptible

/ˌɪmpərˈsɛptəbəl/
adjective
  1. Impossible or extremely difficult to notice or detect using the senses.
    • She made an imperceptible nod to signal her agreement.
    • The glacier's movement is imperceptible over a single day.
    • The difference in temperature was imperceptible to the human hand.
  2. Very slight or gradual, so as to be barely noticeable.
    • Over years, the imperceptible erosion wore down the mountain.
    • There was an imperceptible shift in his mood as the conversation went on.
    • The imperceptible change in the color of the sky signaled the approaching dawn.
What does "imperceptible" mean? | whatsthatwordmean | whatsthatwordmean