IPA: //sʌbˈtrɒpɪkəl//
KK: /sʌbˈtrɒpɪkəl/
Relating to regions that are near the Tropics, typically characterized by warm temperatures and distinct seasons.
The subtropical climate is ideal for growing a variety of fruits and vegetables.
Subtropical is formed from "sub-" (meaning under or below) and "tropical" (from Latin "tropicus", meaning pertaining to the tropics). The word describes regions that are located just below the tropical zone, hence, under the tropics.
Think of being 'under' ('sub-') the 'tropics' — that's why subtropical refers to areas just below the tropical regions.