The word(s) "strengthen" appears 9 time(s) in 9 verse(s) in Quran in Mohsin Khan translation.

(1) And if We had ordered them (saying), "Kill yourselves (i.e. the innocent ones kill the guilty ones) or leave your homes," very few of them would have done it; but if they had done what they were told, it would have been better for them, and would have strengthened their (Faith);

(2) (Remember) when He covered you with a slumber as a security from Him, and He caused water (rain) to descend on you from the sky, to clean you thereby and to remove from you the Rijz (whispering, evil-suggestions) of Shaitan (Satan), and to strengthen your hearts, and make your feet firm thereby.

(3) And remember when you were few and were reckoned weak in the land, and were afraid that men might kidnap you, but He provided a safe place for you, strengthened you with His Help, and provided you with good things so that you might be grateful.

(4) If you help him (Muhammad صلى الله عليه وسلم) not (it does not matter), for Allah did indeed help him when the disbelievers drove him out, the second of the two; when they (Muhammad صلى الله عليه وسلم and Abu Bakr رضي الله عنه) were in the cave, he (صلى الله عليه وسلم) said to his companion (Abu Bakr رضي الله عنه): "Be not sad (or afraid), surely Allah is with us." Then Allah sent down His Sakinah (calmness, tranquillity, peace) upon him, and strengthened him with forces (angels) which you saw not, and made the word of those who disbelieved the lowermost, while the Word of Allah that became the uppermost; and Allah is All-Mighty, All-Wise.

(5) Say (O Muhammad صلى الله عليه و سلم) Ruh-ul-Qudus [Jibril (Gabriel)] has brought it (the Qur'an) down from your Lord with truth, that it may make firm and strengthen (the Faith of) those who believe, and as a guidance and glad tidings to those who have submitted (to Allah as Muslims).

(6) And those who disbelieve say: "Why is not the Qur'an revealed to him all at once?" Thus (it is sent down in parts), that We may strengthen your heart thereby. And We have revealed it to you gradually, in stages. (It was revealed to the Prophet صلى الله عليه وسلم in 23 years.).

(7) And the heart of the mother of Musa (Moses) became empty [from every thought, except the thought of Musa (Moses)]. She was very near to disclose his (case, i.e. the child is her son), had We not strengthened her heart (with Faith), so that she might remain as one of the believers.

(8) Allah said: "We will strengthen your arm through your brother, and give you both power, so they shall not be able to harm you: with Our Ayat (proofs, evidence, verses, lessons, signs, revelations, etc.), you two as well as those who follow you will be the victors."

(9) You (O Muhammad صلى الله عليه وسلم) will not find any people who believe in Allah and the Last Day, making friendship with those who oppose Allah and His Messenger (Muhammad صلى الله عليه وسلم), even though they were their fathers or their sons or their brothers or their kindred (people). For such He has written Faith in their hearts, and strengthened them with Ruh (proofs, light and true guidance) from Himself. And He will admit them to Gardens (Paradise) under which rivers flow to dwell therein (forever). Allah is pleased with them, and they with Him. They are the Party of Allah. Verily, it is the Party of Allah that will be the successful.