A person who concentrates primarily on a particular subject or activity; a person highly skilled in a specific and restricted field. The hospital hired a specialist to handle complex cardiac surgeries.
A military rank in the U.S. Army, above private first class and below corporal. After completing his training, he was promoted to the rank of specialist.
An organism that is highly adapted to a particular environment or food source and therefore has a narrow ecological niche. The koala is a feeding specialist that subsists almost exclusively on eucalyptus leaves.