The word(s) "skeptic" appears 2 time(s) in 2 verse(s) in Quran in Saheeh International translation.

(1) Their building which they built will not cease to be a [cause of] skepticism in their hearts until their hearts are stopped. And Allah is Knowing and Wise.

(2) And Joseph had already come to you before with clear proofs, but you remained in doubt of that which he brought to you, until when he died, you said, 'Never will Allah send a messenger after him.' Thus does Allah leave astray he who is a transgressor and skeptic."