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

(21) Do they not reflect? Their companion is not seized with madness: he is but a perspicuous warner.

(22) Say: "I have no power over any good or harm to myself except as Allah willeth. If I had knowledge of the unseen, I should have multiplied all good, and no evil should have touched me: I am but a warner, and a bringer of glad tidings to those who have faith."

(23) Say to the Unbelievers, if (now) they desist (from Unbelief), their past would be forgiven them; but if they persist, the punishment of those before them is already (a matter of warning for them).

(24) Is it a matter of wonderment to men that We have sent Our inspiration to a man from among themselves?- that he should warn mankind (of their danger), and give the good news to the Believers that they have before their Lord the lofty rank of truth. (But) say the Unbelievers: "This is indeed an evident sorcerer!"

(25) They rejected Him, but We delivered him, and those with him, in the Ark, and We made them inherit (the earth), while We overwhelmed in the flood those who rejected Our Signs. Then see what was the end of those who were warned (but heeded not)!

(26) Why was there not a single township (among those We warned), which believed,- so its faith should have profited it,- except the people of Jonah? When they believed, We removed from them the penalty of ignominy in the life of the present, and permitted them to enjoy (their life) for a while.

(27) Say: "Behold all that is in the heavens and on earth"; but neither Signs nor warners profit those who believe not.

(28) (It teacheth) that ye should worship none but Allah. (Say): "Verily I am (sent) unto you from Him to warn and to bring glad tidings:

(29) Perchance thou mayest (feel the inclination) to give up a part of what is revealed unto thee, and thy heart feeleth straitened lest they say, "Why is not a treasure sent down unto him, or why does not an angel come down with him?" But thou art there only to warn! It is Allah that arrangeth all affairs!

(30) We sent Noah to his people (with a mission): "I have come to you with a Clear warning: