IPA: //sʌbˈspɛʃəlɪst//
KK: /sʌbˈspɛʃəlɪst/
A professional who focuses on a specific area within a broader field of expertise.
The subspecialist was called in to provide expert advice on the rare condition.
Subspecialist → It is formed from "sub-" (meaning under or below) and "specialist" (from Latin "specialis", meaning particular or specific). The word refers to a specialist who focuses on a specific area within a broader field, thus being an expert in a narrower domain.
Think of someone who is an expert 'under' ('sub-') a larger field of knowledge — that's why a subspecialist is a specialist in a specific area.