IPA: //ʌnˈsiː.zən.ə.bəl//
KK: /ʌnˈsiːzənəbl/
Not typical for the current time of year, often referring to weather or conditions that are unusual for a particular season.
The unseasonable warmth in December surprised everyone.
Comparative: more unseasonable
Superlative: most unseasonable
Unseasonable → It is formed from "un-" (meaning not) and "season" (from Old French *saison*, meaning a time or period). The word "unseasonable" means not appropriate for the time or season.
Think of 'not' ('un-') being combined with a 'time' or 'period' ('season') — that's why unseasonable refers to something that is not suitable for the current time.