Thought I had better put in an appearance before poor old BTW expired out of loneliness. Things have been busy.
Random dictionary delve – sombrero is Spanish for any hat, but the word has been – borrowed? misused? – to mean the wide brimmed one. Similarly, avon is assumed to mean river, in ancient languages current around the British Isles when the various invaders/town planners showed up, hence the superfluity of such named water courses. And, of course, the hidden irony of the tautology.
My dad loved word play and entymology, and superfluity would have got his day off to a good start.