Kaaf Haa Yaa ‘Ain Saad
Firstly, this is from the mutashabihat so Allah (swt) alone, and no one else, knows the true meaning of it. But nevertheless, the following is mentioned in al-Jami’ li Ahkaam al-Qur’an of Imam al-Qurtubi:
ibn ‘Abbas said concerning ‘Kaaf Haa Yaa ‘Ain Saad‘: “The kaaf is from Kaafin (Sufficient), the haa is from Haadin (Guide), the yaa is from Hakeem (Wise), the ‘ain is from ‘Aleem (All-Knowing), and the saad is from Saadiq (True).” ibn ‘Azeez al-Qushairi mentioned it from ibn ‘Abbas.
It’s meaning is: “Sufficient (Kaafin) for His creation, a Guide (Haadin) for His slaves, His Yad is over their hands, Cognizant (‘Aalimun) of them, Truthful (Saadiqun) in His promise.” al-Tha’labi mentioned it from al-Kalbi and al-Suddi and Mujahid and Dahhak.
And al-Kalbi also said: “The kaaf is from Kareem (Noble), Kabeer (Great), and Kaafin (Sufficient); the haa is from Haadin (Guide); the yaa is from Raheem (Merciful); the ‘ain is from ‘Aleem (All-Knowing) and ‘Azeem (Supreme); and the saad is from Saadiq (True): and the meaning is one.”
And also from ibn ‘Abbas: “It is a name from the Names of Allah (swt).” From ‘Ali (ra): “It is a name of Allah, azza wa jall” and he used to say: “O Kaaf Haa Yaa ‘Ain Saad! Forgive me.” al-Ghaznawi mentioned it. al-Suddi: “It is the greatest name of Allah, which if He is asked by it, He gives. And if He is called upon by it, He answers.”