Is there any generally accepted definition … or is it a free for all?

I think I can see to which end of the scale it is tending! (Carefully handling the preposition).

Thank you all for the information. There are some surprises there, particularly in the Washington State situation, but I guess historical reasons prevail as they do over here. In general I think the decisions seem to be based on much the same guidelines as here – where at one time you needed a cathedral to be a city, but that changed some time back. In case anyone is interested this link includes the factors involved in making a new city in the UK.

http://www.lcd.gov.uk/constitution/city/cityhome.htm