IPA: /ˈtrɛndˌsɛtə/
KK: /ˈtrɛndˌsɛtər/
A person who creates or popularizes new styles, ideas, or trends, especially in fashion or culture.
She is known as a trendsetter in the fashion industry, always wearing the latest styles before they become popular.
Trendsetter → It is formed from "trend" (from Middle English *trende*, meaning a course or direction) and "setter" (from Old English *settan*, meaning to place or put). A trendsetter is someone who places or establishes a new direction or style that others follow.
Think of someone who 'places' ('setter') a new 'direction' ('trend') in fashion or behavior — that's why a trendsetter is someone who starts new trends.