This is the 11283rd most frequent Russian word.
декабрьского
"Of December."
The word 'декабрьского' here is used as a genitive singular possessive adjective, describing an entity (wind) related to December.
Мы встретили холодное утро декабря прямо на декабрьского ветра берегу.
We encountered a cold December morning on the December wind's shore.
The word 'декабрьского' is used attributively to describe a specific day belonging to or characterized by December in genitive singular form.
В декабрьского день солнце садилось особенно рано.
In a December's day, the sun set particularly early.
'декабрьского' acts as a modifier for 'чая' (tea), indicating the tea is associated with December in flavor or occasion, using genitive singular form.