Definition of “expert” - Learner’s Dictionary

expert

noun [ C ] us uk /ˈekspɜːt/
Extra Examples
an independent experta martial arts expertI'm not an expert by any means.When it comes to baking cakes, she's an expert.He's an expert in the field of biochemistry.

B1 someone who has a lot of skill in something or a lot of knowledge about something:

He's an expert on Japanese literature.
Show me how to use this computer - You're the expert.

(Definition of “expert noun” from the Cambridge Learner's Dictionary © Cambridge University Press)