The word(s) "vain" appears 38 time(s) in 38 verse(s) in Quran in Abdullah Yusuf Ali translation.

(31) Even if the wrong-doers had all that there is on earth, and as much more, (in vain) would they offer it for ransom from the pain of the Penalty on the Day of Judgment: but something will confront them from Allah, which they could never have counted upon!

(32) Now then, for that (reason), call (them to the Faith), and stand steadfast as thou art commanded, nor follow thou their vain desires; but say: "I believe in the Book which Allah has sent down; and I am commanded to judge justly between you. Allah is our Lord and your Lord: for us (is the responsibility for) our deeds, and for you for your deeds. There is no contention between us and you. Allah will bring us together, and to Him is (our) Final Goal.

(33) Then seest thou such a one as takes as his god his own vain desire? Allah has, knowing (him as such), left him astray, and sealed his hearing and his heart (and understanding), and put a cover on his sight. Who, then, will guide him after Allah (has withdrawn Guidance)? Will ye not then receive admonition?

(34) O ye who believe! Obey Allah, and obey the messenger, and make not vain your deeds!

(35) O ye who believe! Raise not your voices above the voice of the Prophet, nor speak aloud to him in talk, as ye may speak aloud to one another, lest your deeds become vain and ye perceive not.

(36) In order that ye may not despair over matters that pass you by, nor exult over favours bestowed upon you. For Allah loveth not any vainglorious boaster,-

(37) So leave them to plunge in vain talk and play about, until they encounter that Day of theirs which they have been promised!-

(38) "But we used to talk vanities with vain talkers;