The word(s) "warn" appears 140 time(s) in 128 verse(s) in Quran in Abdullah Yusuf Ali translation.

(11) And this is a Book which We have sent down, bringing blessings, and confirming (the revelations) which came before it: that thou mayest warn the mother of cities and all around her. Those who believe in the Hereafter believe in this (Book), and they are constant in guarding their prayers.

(12) "O ye assembly of Jinns and men! came there not unto you messengers from amongst you, setting forth unto you My signs, and warning you of the meeting of this Day of yours?" They will say: "We bear witness against ourselves." It was the life of this world that deceived them. So against themselves will they bear witness that they rejected Faith.

(13) (The messengers were sent) thus, for thy Lord would not destroy for their wrong-doing men's habitations whilst their occupants were unwarned.

(14) A Book revealed unto thee,- So let thy heart be oppressed no more by any difficulty on that account,- that with it thou mightest warn (the erring) and teach the Believers).

(15) "Do ye wonder that there hath come to you a message from your Lord, through a man of your own people, to warn you,- so that ye may fear Allah and haply receive His Mercy?"

(16) "Do ye wonder that there hath come to you a message from your Lord through a man of your own people, to warn you? call in remembrance that He made you inheritors after the people of Noah, and gave you a stature tall among the nations. Call in remembrance the benefits (ye have received) from Allah: that so ye may prosper."

(17) So We exacted retribution from them: We drowned them in the sea, because they rejected Our Signs and failed to take warning from them.

(18) Those who behave arrogantly on the earth in defiance of right - them will I turn away from My signs: Even if they see all the signs, they will not believe in them; and if they see the way of right conduct, they will not adopt it as the way; but if they see the way of error, that is the way they will adopt. For they have rejected our signs, and failed to take warning from them.

(19) When they disregarded the warnings that had been given them, We rescued those who forbade Evil; but We visited the wrong-doers with a grievous punishment because they were given to transgression.

(20) Many are the Jinns and men we have made for Hell: They have hearts wherewith they understand not, eyes wherewith they see not, and ears wherewith they hear not. They are like cattle,- nay more misguided: for they are heedless (of warning).