Imperceptible

Part of speech: adjective (a.)

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.