From the Arabic root ك-ت-ب (k-t-b), meaning "to write." The root gives rise to a rich family of words: كَتَبَ (kataba, "he wrote"), كَاتِب (kātib, "writer/clerk"), مَكْتَبَة (maktaba, "library/bookstore"), and مَكْتَب (maktab, "office/desk"). The same Semitic root is echoed in Hebrew כָּתַב (katav, "to write"), highlighting the deep shared heritage of Semitic languages.

The word كِتَاب holds profound cultural and religious weight in the Arab world. Al-Qurʾān is referred to as الكِتَاب (The Book) par excellence, and Muslims, Christians, and Jews are collectively called أَهْل الكِتَاب (Ahl al-Kitāb, "People of the Book"). In everyday life, the word covers everything from school textbooks to novels. Note that in some dialects (e.g., Egyptian Arabic), كِتَاب may be pronounced "kitāb" while the plural كُتُب (kutub) is universally understood. False friend alert for Urdu/Persian learners: کتاب (kitāb) in those languages means exactly the same thing, borrowed directly from Arabic.