from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. Not noticeably, too small to be detected, too little to be perceived.
from The Century Dictionary and Cyclopedia
- In an imperceptible manner; so as not to be perceived.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adv. in an imperceptible manner or to an imperceptible degree
imperceptible + -ly (Wiktionary)