1An eye (with reference to its ability to see); a functioning eye, especially as opposed to one that is blind or has impaired vision.

2In singular and (occasionally) in plural. An ability to see things clearly, especially more clearly than most people; the quality of being observant, perceptive, or insightful.

Sometimes as part of an extended metaphor, especially with reference to Proverbs 20:12 ‘The hearing eare, and the seeing eye, the Lord hath made euen both of them’.

1US Designating a dog trained to help blind and visually impaired people move around safely, by guiding them around obstacles and through crowds, negotiating traffic, etc. Frequently in "seeing-eye dog".

The organization The Seeing Eye, which breeds and trains puppies to become guide dogs, was established in 1929. In the United States Seeing Eye is a trademark for guide dogs.

2Baseball
Designating a ball hit into the field which eludes fielders as if it can see them; of or relating to such balls.