Sentence:  “... I hope you will still lay an additional obligation upon the Count, by retorting the vengeance of the law upon his perfidious accuser, whom I know to be a trader in those articles of merchandise which are prohibited by the ordinances of this nation. I have seen him lately at Boulogne, and am perfectly well acquainted with some persons who have supplied him with French lace and embroidery; and, as a proof of what I allege, I desire you will order him and this barber, who is his <WSD>understrapper</WSD>, to be examined on the spot.” 
Meaning of the word marked with <WSD> tags:  Any underling or inferior in office.