A consultant would do research and give advice on a job, a subcontractor would actually do part of the job. Most modern manufacturing is done using many subcontractors to build everything necessary...
Specialty registrar is the grade undertaken, typically in hospitals, after completion of foundation training. Specialty registrars train in a specialist area and develop the skills and knowledge...
These are terms used in the UK and Commonwealth :), in case you are American. Everyone who has a medical degree is called a doctor. If you are registered with the GMC, you are allowed to practice....
Consider the Old West - an external consultant is like the hired gun that comes into town because yo have an extreme and unusual set of outlaws making your town their home, he shoots the bad guys,...