Imperceptible, a.
Etymology: [Pref. im- not + perceptible: cf. F. imperceptible.]
Not perceptible; not to be apprehended or cognized by the souses; not discernible by the mind; not easily apprehended. Almost imperceptible to the touch. Dryden. Its operation is slow, and in some cases almost imperceptible. Burke. -- Im`per*cep"ti*ble*ness, n. -- Im`per*cep"ti*bly, adv. Their . . . subility and imperceptibleness. Sir M. Hale.
Shades of meaning
Fernald lists imperceptible only as an antonym, under evident.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given