blind spot

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Anatomy The small, circular, optically insensitive region in the retina where fibers of the optic nerve emerge from the eyeball. It has no rods or cones. Also called optic disk.
2. n. A part of an area that cannot be directly observed under existing circumstances.
3. n. An area where radio reception is weak or nonexistent.
4. n. A subject about which one is markedly ignorant or prejudiced: "Of course, all of us . . . have our crotchets and our blind spots. I abhor novels written in the present tense” ( Mordecai Richler).

Wiktionary

1. n. The place where the optic nerve attaches to the retina, and so where the retina cannot detect light.
2. n. In driving, the part of the road that cannot be seen in the rear-view mirror.
3. n. figuratively An inability to recognize a fact or think clearly about a certain topic, especially because of a prejudice.
4. n. A location where radio reception and/or transmission is significantly poorer than in surrounding locations.

GNU Webster's 1913

1. adj. (Anat.) the point in the retina of the eye where the optic nerve enters, and which is insensible to light.

WordNet 3.0

1. n. the point where the optic nerve enters the retina; not sensitive to light
2. n. a subject about which you are ignorant or prejudiced and fail to exercise good judgment