The word(s) "secret" appears 51 time(s) in 49 verse(s) in Quran in Abdullah Yusuf Ali translation.

(31) This, because they said to those who hate what Allah has revealed, "We will obey you in part of (this) matter"; but Allah knows their (inner) secrets.

(32) "Verily Allah knows the secrets of the heavens and the earth: and Allah Sees well all that ye do."

(33) Or have they a ladder, by which they can (climb up to heaven and) listen (to its secrets)? Then let (such a) listener of theirs produce a manifest proof.

(34) He merges Night into Day, and He merges Day into Night; and He has full knowledge of the secrets of (all) hearts.

(35) Seest thou not that Allah doth know (all) that is in the heavens and on earth? There is not a secret consultation between three, but He makes the fourth among them, - Nor between five but He makes the sixth,- nor between fewer nor more, but He is in their midst, wheresoever they be: In the end will He tell them the truth of their conduct, on the Day of Judgment. For Allah has full knowledge of all things.

(36) Turnest thou not thy sight towards those who were forbidden secret counsels yet revert to that which they were forbidden (to do)? And they hold secret counsels among themselves for iniquity and hostility, and disobedience to the Messenger. And when they come to thee, they salute thee, not as Allah salutes thee, (but in crooked ways): And they say to themselves, "Why does not Allah punish us for our words?" Enough for them is Hell: In it will they burn, and evil is that destination!

(37) O ye who believe! When ye hold secret counsel, do it not for iniquity and hostility, and disobedience to the Prophet; but do it for righteousness and self-restraint; and fear Allah, to Whom ye shall be brought back.

(38) secret counsels are only (inspired) by the Evil One, in order that he may cause grief to the Believers; but he cannot harm them in the least, except as Allah permits; and on Allah let the Believers put their trust.

(39) Allah is He, than Whom there is no other god;- Who knows (all things) both secret and open; He, Most Gracious, Most Merciful.

(40) O ye who believe! Take not my enemies and yours as friends (or protectors),- offering them (your) love, even though they have rejected the Truth that has come to you, and have (on the contrary) driven out the Prophet and yourselves (from your homes), (simply) because ye believe in Allah your Lord! If ye have come out to strive in My Way and to seek My Good Pleasure, (take them not as friends), holding secret converse of love (and friendship) with them: for I know full well all that ye conceal and all that ye reveal. And any of you that does this has strayed from the Straight Path.