imperceptible

not perceptible by a sense or by the mind <a slight difference in hue between the two glasses that's imperceptible unless they're placed side by side> Synonyms impalpable, inappreciable, indistinguishable, insensible Related Words inaudible, intangible, invisible; inconspicuous, indistinct, unnoticeable, unseeable, unseen; faint, insignificant, liminal, slender, slight, subtle, trivial; buried, concealed, covert, disguised, hidden, obscure, shrouded, unapparent, vague Near Antonyms audible, observable, recognizable, tangible, visible; clear, conspicuous, evident, eye-catching, manifest, noticeable, obvious, plain, prominent, striking; apparent, distinct, significant, straightforward Antonyms appreciable, discernible (also discernable), palpable, perceptible, ponderable, sensible