someone with Particular information, talent, or teaching in anything a computer/clinical expert expert (at/in/on one thing) an expert in boy or girl psychology an expert on present day literature expert (at/in/on performing a thing) He's an expert at having his very own way. Don't question me—I am no expert! https://cnetnews.co.uk/2024/08/16/expert-insights-choosing-the-right-copyright-dispute-lawyer-in-the-uk/