Much depends on the point at which we decide that RP came into existence. William Gladstone, who was PM for four different terms in the late 19th century, went to Eton College yet his pronunciation gave away that he was from the North of England and his speech was criticised by RP speakers in the early 20th century.
Definition of vane. 1a : a movable device attached to an elevated object (as a spire) for showing the direction of the windb : one that is changeable or inconstant.
: a movable device usually attached to a roof to show which way the wind is blowing. See words that rhyme with weather vane Spanish Central: Translation of weather vane Nglish: Translation of weather vane for Spanish speakers Britannica.com: Encyclopedia article about weather vane.