Main Entry: in·cred·u·lous

Pronunciation: \(ˌ)in-ˈkre-jə-ləs, -dyə-ləs\

Function: adjective

Etymology: Latin incredulus, from in- + credulus credulous

Date: 1579

1 : unwilling to admit or accept what is offered as true : not credulous : skeptical
2 : incredible 1
3 : expressing incredulity <an incredulous stare>

— in·cred·u·lous·ly adverb

usage Sense 2 was revived in the 20th century after a couple of centuries of disuse. Although it is a sense with good literary precedent—among others Shakespeare used it—many people think it is a result of confusion with incredible, which is still the usual word in this sense.