/ˈekspɜːrt/ ​a person with special knowledge, skill or training in something. a legal/security/medical/computer expert.

a person with special knowledge, skill, or training in something; a computer/medical expert; expert (at/in/on something); an expert in child psychology.

​done with, having or involving great knowledge or skill. to seek expert advice; Only a fully qualified doctor can give an expert opinion. an expert witness ...

The earliest known use of the verb expert is in the Middle English period (1150—1500). OED's earliest evidence for expert is from before 1475, ...

done with, having, or involving great knowledge or skill; to seek expert advice/an expert opinion; an expert driver.

/ˌekspɜːrˈtiːz/ [uncountable] ​expert knowledge or skill in a particular subject, activity or job.

[uncountable] expert knowledge or skill in a particular subject, activity, or job professional/scientific/technical, etc.

a person with a high level of knowledge or skill relating to a particular subject or activity: a gardening/medical expert.

a person who is an expert in a particular area of work or study; a specialist in Japanese history.

​in a way that shows or involves great knowledge or skill. The roads were icy but she stopped the car expertly. The music was expertly performed.