This is the 14159th most frequent Turkish word.
mührünün
"His/her/its seal" or "his/her/its stamp."
Here, "mührünün" is used as a possessive construction meaning "its stamp," implying that the book has a stamp, and the detail of this stamp is noteworthy.
Kitabın sonundaki mührünün detayı benim dikkatimi çekti.
The detail of the stamp at the end of the book caught my attention.
In this sentence, "mührünün" signifies the possession of the seal by the king, translating to "the king's seal."
Kralın mührünün benzersiz bir deseni vardı.
The king's seal had a unique design.
Here, "mührünün" again indicates possession, referring to the required stamp as belonging to the entity which issued the document.