What's the difference between citizen and a subject?

[plowter]

Constitutionally, residents of the UK are subjects of HM Queen. What's the difference between a citizen and a subject?

[Whickerman]

A citizen is "a native or naturalized member of a state or nation who owes allegiance to its government and is entitled to its protection"

A subject is "a person who is under the dominion or rule of a sovereign"

I am an Irish citizen. I am not however, a subject with alliegance to any sovereign. As a UK citizen, you are both. Neither is exclusive.

BTW - there's a lot of talk about constitutionality in the UK, however there isn't an actual document in existence that can be held up as the British Constitution. Instead it's a mish mash of laws form the following sources:
Statutes such as the Magna Carta of 1215 and the Act of Settlement of 1701.
Laws and Customs of Parliament; political conventions
Case law; constitutional matters decided in a court of law.