This is the 9187th most frequent Russian word.
синеникольского
The word "синеникольского" appears to be a complex form potentially derived from "Синеникольский," which could relate to a proper noun, such as a place or name, meaning "of or pertaining to Sinenikolsky."
Here, "синеникольского" is used as an adjective describing the period associated with a proper name or historical context.
Старинный храм синеникольского периода привлекает множество туристов.
The ancient temple from the Sinenikolskiy period attracts many tourists.
In this case, "синеникольского" delineates a specific people or ethnicity connected to the term mentioned.
Книга повествует о жизни синеникольского народа.
The book narrates the life of the Sinenikolskiy people.
The use here suggests items originating from or tied to a location, era, or cultural aspect described by "синеникольского".