The word(s) "doubt" appears 83 time(s) in 77 verse(s) in Quran in Mohsin Khan translation.

(31) As if they had never lived there. No doubt! Verily, Thamud disbelieved in their Lord. So away with Thamud!

(32) Verily, Ibrahim (Abraham) was, without doubt, forbearing, used to invoking Allah with humility, and was repentant (to Allah all the time, again and again).

(33) So be not in doubt (O Muhammad صلى الله عليه و سلم) as to what these people (pagans and polytheists) worship. They worship nothing but what their fathers worshipped before (them). And verily, We shall repay them in full their portion without diminution.

(34) Indeed, We gave the Book to Musa (Moses), but differences arose therein, and had it not been for a Word that had gone forth before from your Lord, the case would have been judged between them, and indeed they are in grave doubt concerning it (this Qur'an).

(35) Has not the news reached you, of those before you, the people of Nuh (Noah), and 'Ad, and Thamud? And those after them? None knows them but Allah. To them came their Messengers with clear proofs, but they put their hands in their mouths (biting them from anger) and said: "Verily, we disbelieve in that with which you have been sent, and we are really in grave doubt as to that to which you invite us (i.e. Islamic Monotheism)."

(36) Their Messengers said: "What! Can there be a doubt about Allah, the Creator of the heavens and the earth? He calls you (to Monotheism and to be obedient to Allah) that He may forgive you of your sins and give you respite for a term appointed." They said: "You are no more than human beings like us! You wish to turn us away from what our fathers used to worship. Then bring us a clear authority (i.e. a clear proof of what you say)."

(37) They said: "Nay, we have come to you with that (torment) which they have been doubting.

(38) They assign to Allah that which they dislike (for themselves), and their tongues assert the falsehood that the better things will be theirs. No doubt for them is the Fire, and they will be the first to be hastened on into it, and left there neglected. (Tafsir Al-Qurtubi)

(39) No doubt, in the Hereafter, they will be the losers.

(40) See they not that Allah, Who created the heavens and the earth, is Able to create the like of them. And He has decreed for them an appointed term, whereof there is no doubt. But the Zalimun (polytheists and wrong-doers) refuse (the truth - the Message of Islamic Monotheism, and accept nothing) but disbelief.