Related Clues:

• Part of a cardboard box
• Cold-weather cap attachment
• Entrance at a bivouac, perhaps
• Plane-wing part
• Dog door, often
• Mud catcher
• Book jacket foldover
• Dr. Dentons feature
• Wing feature
• Do part of the chicken dance
• Beat, as wings
• It protects a drum from a wind
• Tent door
• Try to stay up?
• Winter protection