from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A fixed signal at the entrance to a railroad block, indicating whether or not trains may enter.
from the GNU version of the Collaborative International Dictionary of English
- One of the danger signals or safety signals which guide the movement of trains in a block system. The signal is often so coupled with a switch that act of opening or closing the switch operates the signal also.
from The Century Dictionary and Cyclopedia
- n. An automatic signal placed at one end of a section of a railroad to block the section by warning trains coming into it of the presence in it of another train.
Sorry, no etymologies found.