This is the 12694th most frequent Polish word.
niemiecką
"Niemiecką" means "German" (feminine adjective, accusative case).
The word 'niemiecką' is used here as an adjective describing the book. The ending '-ą' corresponds to the accusative singular feminine form, matching the noun 'książkę' (book).
Mam niemiecką książkę.
I have a German book.
Here, 'niemiecką' is an attribute modifying 'dokładnością' which is in the instrumental case. This shows the connection of the adjective's form with the grammatical case of the noun it modifies.
Ona mówi z niemiecką dokładnością.
She speaks with German precision.
In this example, 'niemiecką' again serves as an adjective. The ending signals agreement with 'decyzję' (decision), which is accusative singular feminine.