The word(s) "weaken" appears 2 time(s) in 2 verse(s) in Quran in Abdullah Yusuf Ali translation.

(1) How many of the prophets fought (in Allah's way), and with them (fought) Large bands of godly men? but they never lost heart if they met with disaster in Allah's way, nor did they weaken (in will) nor give in. And Allah Loves those who are firm and steadfast.

(2) We only send the messengers to give Glad Tidings and to give warnings: But the unbelievers dispute with vain argument, in order therewith to weaken the truth, and they treat My Signs as a jest, as also the fact that they are warned!