a person who concentrates primarily on a particular subject or activity; a person highly skilled in a specific and restricted field.
a physician highly trained in a particular branch of medicine.
(in the US Army) an enlisted person of one of four grades ( specialist 4, equivalent to the rank of corporal, being the most junior, specialist 7, equivalent to sergeant first class, being the most senior) who has technical or administrative duties but does not exercise command.
possessing or involving detailed knowledge or study of a restricted topic:the project may involve people with specialist knowledge
[attributive] concentrating on a restricted field, market, or area of activity:a specialist electrical shop