Kitab (Arabic: کتاب, kitāb), also transcribed kitaab, is the Arabic word for "a book".
This question is similar to many other fiqhi questions, where one would need to refer to his/her Marja' taqleed.
That being said, according to the view of most of our esteemed jurists, Ahlul Kitab are not najis, and as for temporary marriage with a Kitabiyah woman, most Maraji' also deem it as halal.
And Allah knows best.
Kitab in Arabic language means book, but in these verses in Quran it means the Divine knowledge revealed from Allah ( SWT).