'Imperceptibly' definitions:

Definition of 'imperceptibly'

From: WordNet
adverb
In an imperceptible manner or to an imperceptible degree; "the power of the Secretary of State in London increased gradually but imperceptibly" [syn: imperceptibly, unnoticeably] [ant: noticeably, observably, perceptibly]

Definition of 'Imperceptibly'

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]