As Salaamu Alaikum Wa Rahmatullaahi Wa Barakatuhu
As we know that in Urdu means book. But have you ever heard this in Arabic as well? Yes, ofcourse! In fact many times while reading Qur'aan we encounter this word and it has been adopted from Arabic into Urdu.
So now you know what does Kitaab means, isn't it?
Let me tell some thing more. What are those two spoons or sticks, which you find at the end of most of the arabic words? These are called TANWEEN. Strike a steel spoon against other and you will get the sound they produce. (t)un, (t)an, (t)in.
Spoon is default tool for eating Maggi (unless you are Chinese), so is un sound default ending for most of arabic words (unless there is a reason to change it to stick(s) or an exeption).
So if you pronounce Kitaab completely, you will pronounce it as Kitaabun and it will mean A BOOK.