An opening or hole through which you look, like the holes in a mask, helmet, or piece of armor.
From 'eye' + 'hole' (Old English hol). Used at least since medieval times to describe openings in protective gear designed for vision.
Halloween masks with eyeholes are positioned slightly higher than actual eye level—mask designers do this on purpose because when you're looking straight ahead at eye level, you actually see slightly upward from your eye socket.
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