This is the 9444th most frequent Turkish word.
adlarını
"Their names."
The word 'adlarını' here means 'their names', referring to the names of the characters in the book. The possessive suffix '-ların' denotes 'their', and the accusative case '-ı' indicates the direct object.
Kitaptaki karakterlerin adlarını öğrendik.
We learned the names of the characters in the book.
In this sentence, 'adlarını' refers to 'their names', applying to the cities mentioned. The construction follows the possessive and accusative structure as explained.
Bütün şehirlerin adlarını ezberlemek zorunda kaldım.
I had to memorize the names of all the cities.
Here, 'adlarını' is used similarly to indicate 'their names', referring to the names of the pets. The possessive and accusative cases are present just like in the previous examples.