Arabic root words are three consonants that provide the base meaning of a word. These root words are morphed into various words by adding vowels, prefixes and suffixes. The words have related meanings to the root words. For example, the root k-t-b means marking, inscribing or writing, and it can form words like "to write", "book" and "office". The words of Quran are linked to a dictionary that shows the root words and their meanings.
An office is a place where you write and a book is a result of writing. These words are related by meaning, but also by the root. You can hear and see that three letters are the same in all the words:
The words "to write", "book" and "office" have the root letters (k) ك, (t) ت and (b) ب ' '
Quite a few Arabic word has the root k t b.
kataba he wrote
katabū they wrote
katabat she wrote
katabnā we wrote
Similarly, there are simple and predictable rules for present (imperfect) and imperative forms of the basic root, such as:
yaktubu he writes
yaktabunā they write
taktubu you write
naktubu we write
'uktub write!
And then the vastness really begins to be seen as additional forms such as verbal nouns are created from the same simple root k-t-b to describe things such as:
katīb writer
kitāba the act of writing
kitāb some writing, book
kutub books
kutubī bookdealer
kutayyib booklet
maktūb letter
maktab school, office
maktaba library, literature
maktabī individual office
miktāb typewriter
mukātaba correspondence
iktitāb registration
istiktāb dictation
.... and on and on. This is only a limited sample of the immense variety of words that can be formed by simple and predictable usage of the basic root which was only the three consonants k-t-b.