Definition of "outrigger"
An extension mechanism, often retractable when not in use, on a boat, vehicle, or structure which helps to stabilize it to keep it from tipping over.
Quotations
From the cowcatcher hung the outrigger of the tricycle, leaping about as though in the grip of death itself, beating against the iron that had shattered it, striking the road, sending the gravel flying.
1938, Xavier Herbert, chapter XII, in Capricornia, New York: D. Appleton-Century, published 1943, page 200