The root of these six words is:
k – t – b
ك – ت – ب
Now look at the English equivalents for these words. Remember that with nouns the context finally decides what is actually meant.
كتاب kitaab – document, manuscript, book, etc.
كاتب kaatib – writer, author, secretary, etc.
مَكت maktab – office, desk, etc.
كتب kataba – he wrote
يكتب yaktub – he is writing / he writes
مكتبة makataba – library
Remember that the root s – l – m conveys the idea of ‘peace’.
What would you say the root k – t – b conveys?