My question was ill asked.  In the first instance the term  
"economist" is a noun, not an adjective.  In the second, a brief look  
at the Oxford Dictionary delivers the information that the word was  
first used in 1586, but not with the meaning now attached to it.   
Adam Smith used the term in the modern sense in 1776 in a  
reference to "a considerable sect, distinguished in the French  
republic of letters".  Most likely the term was first used precisely  
as we use it by Thorold Rogers in 1866.    
 
Robin Neill