This is the 798th most frequent Azerbaijani word.
məktub
"Letter" (a written message).
In this sentence, 'məktub' is used in its primary meaning, which is 'a letter', referring to a piece of written communication.
O, dostuna məktub yazmışdı.
He had written a letter to his friend.
Here, 'məktub' refers to the act of reading letters as a habitual activity.
Məktub oxumaq onun hər axşam adi halıdır.
Reading a letter is his usual evening routine.
In this usage, 'məktub' is tied to its origin, focusing on identifying who composed the letter.