adj.
Pronunciation: ˌ im-p ə r- ' sep-t ə -b ə l
Function: adjective
Etymology: Middle English, from Middle French, from Medieval Latin imperceptibilis, from Latin in- + Late Latin perceptibilis perceptible
Date: 15th century
: not perceptible by a sense or by the mind : extremely slight, gradual, or subtle < imperceptible differences>
– im · per · cep · ti · bly \ - ' sep-t ə -bl ē \ adverb