The word(s) "delusion" appears 4 time(s) in 4 verse(s) in Quran in Mohsin Khan translation.

(1) And so We have appointed for every Prophet enemies - Shayatin (devils) among mankind and jinn, inspiring one another with adorned speech as a delusion (or by way of deception). If your Lord had so willed, they would not have done it; so leave them alone with their fabrications. (Tafsir Qurtubi)

(2) And when the hypocrites and those in whose hearts is a disease (of doubts) said: "Allah and His Messenger (صلى الله عليه وسلم) promised us nothing but delusion!"

(3) Say (O Muhammad صلى الله عليه وسلم): "Tell me or inform me (what) do you think about your (so-called) partner-gods to whom you call upon besides Allah? Show me, what they have created of the earth. Or have they any share in the heavens? Or have We given them a Book, so that they act on clear proof therefrom? Nay, the Zalimun (polytheists and wrong-doers) promise one another nothing but delusions."

(4) Who is he besides the Most Gracious that can be an army to you to help you? The disbelievers are in nothing but delusion.