Historically in England, a gentleman servant in the
Royal Household who attended the Monarch in a
privy capacity. Though it was a position of high trust and honour, because of its proximity to the fount of power at its most vulnerable, he was literally the officer who attended the monarch sitting on the
stool. He ranked under the
vice-chamberlain. The royal privy apartment would doubtless have been quite
commodious and could accommodate numerous trusty advisers: from such meetings developed the
Privy Council, which still exists as a high organ of state.
The title is also written Groom of the Stole, but stole is in this instance simply a variant of stool, not the ecclesiastical garment, an unrelated word. Though James Boswell (somewhere in his writings, I forget where) would have liked the title to have originally meant a dresser, one who handles stoles the garments, it is alas not.
The court also had other lesser functionaries called Grooms-in-Waiting.
How I would love to enter things for Everything Quests: Support Your Local Library, but sadly, having just crossed the street to my local library, I find they are "no longer a reference library" and do not stock any encyclopaedias or large dictionaries; so these few lines are all you get. They do have a good video collection now though. Ah, progress.