From its role with respect to the two houses of which many legislatures consist
American Heritage Dictionary of the English Language, 5th Edition
Third-house Sentence Examples
In Spain, national pride in the founder aided the Society's cause almost as much as royal patronage did in Portugal; and the third house was opened in Gandia under the protection of its duke, Francisco Borgia, a grandson of Alexander VI.
Those are his quarters, and he pointed to the third house in the village of Gorki.
Thankfully, Saturn has moved on and is now transitioning into your third house.
Gemini is the third sign of the zodiac, so it's no mystery why Geminis love to communicate; Gemini rules the third house of the zodiac.