imperceptibly

adv

1. Not noticeably; such that it cannot be detected, through being too small or too fast, etc.

   “No one noticed that he had moved imperceptibly backwards.”

   “It often happens that the most important results in the natural world are brought about by causes which operate silently, if not imperceptibly.”

   “The moon moved imperceptibly towards setting.”

   “Which means that at the moment Raven entered her, a very small hypodermic needle slipped imperceptibly into the engorged frontal vein of his penis, automatically shooting a cocktail of powerful narcotics and depressants into his bloodstream.”