Of that Peg I confess I've never heard.
A quick search through the books brings this up :

Main Entry: dru·id
Pronunciation: 'drü-id
Function: noun
Usage: often capitalized
Etymology: Latin druides, druidae, plural, from Gaulish druides; akin to Old Irish druí druid, and perhaps to Old English trEow tree
Date: 1563
: one of an ancient Celtic priesthood appearing in Irish and Welsh sagas and Christian legends as magicians and wizards