Specialist
Part of speech: adjective
Definition: Specialised.
Part of speech: noun
Definition: Someone who is an expert in, or devoted to, some specific branch of study or research. A physician whose practice is limited to a particular branch of medicine or surgery. Any of several non-commissioned ranks corresponding to that of corporal.
Consultant
Part of speech: noun
Definition: a person or party that is consulted.a person whose occupation is to be consulted for their expertise, advice, or help in an area or specialty. Alternatively, a party whose business is to be similarly consulted.