Sure looks like it has something to do with vision....but hey, looks like the issue has been remedied with a Websters Dictionary definition and an answer.com website comment. Someone alert the FAA, we can resolve the issue. Always get a chuckle out of Webster definitions and wiki pages being used as "proof". Good stuff.
n.,
pl., lines of sight.
- An imaginary line from the eye to a perceived object.
- An unobstructed path between sending and receiving antennas.