'Imperceptible' definitions:

Definition of 'imperceptible'

From: WordNet
adjective
Impossible or difficult to perceive by the mind or senses; "an imperceptible drop in temperature"; "an imperceptible nod"; "color is unperceivable to the touch" [syn: imperceptible, unperceivable] [ant: perceptible]

Definition of 'Imperceptible'

From: GCIDE
  • Imperceptible \Im`per*cep"ti*ble\, a. [Pref. im- not + perceptible: cf. F. imperceptible.] Not perceptible; not to be apprehended or cognized by the senses; not discernible by the mind; not easily apprehended. [1913 Webster]
  • Almost imperceptible to the touch. --Dryden. [1913 Webster]
  • Its operation is slow, and in some cases almost imperceptible. --Burke. -- {Im`per*cep"ti*ble*ness}, n. -- {Im`per*cep"ti*bly}, adv. [1913 Webster]
  • Their . . . subtilty and imperceptibleness. --Sir M. Hale. [1913 Webster]