noun, noun which may take the genitive case particle 'no'
the coldest season; midwinter
A formal, literary expression used in seasonal greetings or weather descriptions, referring to the period of severe cold.
In this coldest season, I trust you are all doing well.
As we enter the coldest season, please take care of your health.
Compound of 厳寒 (severe cold) + の (possessive particle) + 候 (season, weather). The expression is a set phrase used in formal writing and seasonal greetings.