from the GNU version of the Collaborative International Dictionary of English
- A body of cavalry so called; esp., a British regiment, called the Royal Horse Guards, which furnishes guards of state for the sovereign.
from The Century Dictionary and Cyclopedia
- A body of cavalry for guards. See guard.
- [capitalized] The public office in Whitehall. London, appropriated to the departments under the commander-in-chief of the British army: so called from the two horsemen standing sentry at the gates.
- [capitalized] The military authorities in charge of the war department of Great Britain, in distinction from the civil chief, the Secretary for War.
Sorry, no etymologies found.