3. Any contrivance, especially one having a directing edge, surface, or channel, for giving direction to the motion of anything, as water, an instrument, or part of a machine, or for directing the hand or eye, as of an operator; as: a blade or channel for directing the flow of water to the wheel buckets.
4. A noncommissioned officer or soldier placed on the directiug flank of each subdivision of a column of troops, or at the end of a line, to mark the pivots, formations, marches, and alignments in tactics. Guide bar, an additional rail, between the others, gripped by horizontal driving wheels on the locomotive, as a means of propulsion on steep gradients.