specialist
n. countablen. a person who has a lot of knowledge or skill in one specific area. You see a specialist when you need expert help that a general worker cannot provide.
n. a person who concentrates on a particular subject, activity, or branch of a profession. Often used to distinguish an expert from a generalist or a primary care provider.
The doctor sent me to see a heart specialist.
After the general inspection, the company hired a specialist to fix the complex electrical system.
While a general practitioner manages overall health, a specialist possesses the deep technical expertise required to treat rare or particularly aggressive conditions within a specific organ system.
Borrowed from French spécialiste, equivalent to special + -ist.
Commonly followed by the preposition 'in' to denote the field of expertise.