Robin,
I imagine others will catch this also, but there is a serious mistake
here. Bagehot published his famous _Lombard Street_ in 1873
and was the editor of The Economist for an extended period of time
in the 1800s. Quite sure he was not writing anything in or before
1776. I don't know the earliest usage, but I know that the term
"economist" or "oekonomist" or "economiste" was in use without
the "political" in front in both Germany and France well before it
was in Britain. I would bet France was probably the first place it
was used by itself. BTW, I think it was in France that the term
"economie politique," or its equivalent in whatever language was
also first used.
Barkley Rosser
James Madison University