- a person who is devoted to one subject or to one particular branch of a subject or pursuit.
- a medical practitioner who devotes attention to a particular class of diseases, patients, etc.
- an enlisted person of one of four grades having technical or administrative duties, the grades corresponding to those of corporal through sergeant first class but not requiring the exercise of command.
- a member of an exchange who buys and sells a single stock or a particular group of stocks in their own name or for other stockbrokers and thus helps maintain the market in those securities on that exchange.
- a person who specializes in or devotes himself to a particular area of activity, field of research, etc
- (as modifier)
- an enlisted rank in the US Army denoting technical qualifications that entitle the holder to a noncommissioned officer's pay
- an organism that has special nutritional requirements and lives in a restricted habitat that provides these
