This is the 9679th most frequent Russian word.
черниговскую
"Chernihiv" in adjective form, relating to Chernihiv, a city in Ukraine.
In this sentence, "черниговскую" is an adjective derived from "Чернигов", a city, describing the word "книгу" (book). It indicates that the book relates to Chernihiv.
Я купил черниговскую книгу о местной истории.
I bought a Chernihiv book about local history.
Here, "черниговскую" describes "вышиванку" (embroidered shirt), specifying its style or origin as characteristic of Chernihiv traditions.
Она всегда носит черниговскую вышиванку на праздники.
She always wears the Chernihiv embroidered shirt for celebrations.
In this example, "черниговскую" qualifies "керамику" (ceramics), specifying that these items are from Chernihiv.