simply means a servant or minister. Minstrels were kept in the
service of kings and princes for the entertainment of guests. James
Beattie has a poem in Spenserian verse, called The Minstrel, divided into two books.
The last minstrel of the English stage.
James Shirley, with whom the school of Shakespeare expired.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894