Wiktionary
adv. In an unnoticeable manner.
WordNet
adv. in an imperceptible manner or to an imperceptible degree; "the power of the Secretary of State in London increased gradually but imperceptibly" [syn: imperceptibly, observably] [ant: perceptibly]
Usage examples of "unnoticeably".
In five seconds I could remove the top of his skull and examine his brain in situ, then replace it unnoticeably even to him unless I decided to damage the brain while it was exposed.
She shivered and without separating their faces hitched her body up into his lap, whereupon she garnered his manhood and inserted her other tongues, again almost unnoticeably.
Why, on that particular spring night, did I choose to crawl head first down the wall above the precipice, rather than fly out unnoticeably in the form of a bat, walk less terrifyingly on four legs, or even expectably on two?