A wise and trusted counselor or teacher.
To act as someone's mentor.
Someone who is an expert in, or devoted to, some specific branch of study or research.
A stenotopic species.
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.
An organism that is specialized for a particular environment.
Specialised, involving detailed knowledge of a restricted topic.