Search Result for "imperceptibility": 
Wordnet 3.0

NOUN (1)

1. the property of being imperceptible by the mind or the senses; 



The Collaborative International Dictionary of English v.0.48:

Imperceptibility \Im`per*cep`ti*bil"i*ty\, n.
   The state or quality of being imperceptible.
   [1913 Webster]


WordNet (r) 3.0 (2006):

imperceptibility
    n 1: the property of being imperceptible by the mind or the
         senses [ant: perceptibility]