This is the 5454th most frequent Polish word.
słabej
"Of weak" or "weak" (feminine singular genitive form).
Here 'słabej' is used as an adjective describing the quality of the book.
Mam książkę o słabej jakości.
I have a book of poor quality.
Here 'słabej' is used as an adjective related to the health or physical condition of the dog.
Moja koleżanka ma słabej kondycji psa.
My friend has a dog of weak physical condition.
Here 'słabej' is used to describe the intensity of the reaction, signifying it as weak or muted.