abat-vent

from The Century Dictionary.

• noun A vertical series of sloping roofs or broad slats, inclined outward and downward, forming the filling of a belfry-light, and designed to admit ventilation to the timber frame while protecting the interior from rain and wind, and to direct downward the sound of the bells.
• noun A sloping roof, as that of a penthouse: so named because the slope neutralizes the force of the wind.
• noun Any contrivance designed to act as a shelter or protection from the wind.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A sloping roof.
• noun A metal chimney cap.