A person who is very knowledgeable about or skilful in a particular area
he is an expert in kendo
A person without professional or specialized knowledge in a particular subject
A piece of software which uses databases of expert knowledge to offer advice or make decisions in such areas as medical diagnosis
A person whose level of specialized knowledge or skill in a particular field qualifies them to present their opinion about the facts of a case during legal proceedings
An authority on handwriting; a graphologist.