rail¹ / rāl/ • n. 1. a bar or series of bars, typically fixed on upright supports, serving as part of a fence or barrier or used to hang things on. ∎  (the rails) the inside boundary fence of a racecourse. ∎  the edge of a surfboard or sailboard. ∎  the rim of a billiard or pool table.2. a steel bar or continuous line of bars laid on the ground as one of a pair forming a railroad track: trolley rails. ∎  [often as adj.] railroads as a means of transportation: rail fares traveling by rail.3. a horizontal piece in the frame of a paneled door or sash window. Compare with stile² .4. Electr. a conductor that is maintained at a fixed potential and to which other parts of a circuit are connected.• v. 1. [tr.] provide or enclose (a space or place) with a rail or rails: the altar is railed off from the nave.2. [intr.] (in windsurfing) sail the board on its edge, so that it is at a sharp angle to the surface of the water.PHRASES: go off the rails inf. begin behaving in a strange, abnormal, or wildly uncontrolled way.DERIVATIVES: rail·less adj. rail² • v. [intr.] (rail against/at/about) complain or protest strongly and persistently about: he railed at human fickleness. DERIVATIVES: rail·er n.rail³ • n. a secretive bird (Rallus and other genera) with drab gray and brown plumage, typically having a long bill and found in dense waterside vegetation. The rail family (Rallidae) also includes the crakes, gallinules, moorhens, and coots.