| Switch | Baltimore & Ohio Railroad. |
| Switched | Canada Southern Railroad. |
| Switching | Chicago, Alton & St. Louis Railroad. |
| Swollen | Chicago, Burlington & Quincy Railroad. |
| Swooned | Chicago, Rock Island & Pacific Railroad. |
| Swoop | Chicago & Northwestern Railroad. |
| Sylph | Chicago, Danville & Vincennes Railroad. |
| Sylvan | Grand Trunk Railway |
| Symbol | Great Western Railroad. |
| Symbolic | Illinois Central Railroad. |
| Sympathy | Kansas Pacific Railroad. |
| Symptom | Michigan Central Railroad. |
| Synagogue | Michigan Southern & Lake Shore Railroad |
| Synod | Milwaukee & St. Paul Railroad. |
| Syntax | New York Central Railroad. |
| System | New York & Erie Railroad. |
| Tableau | Pittsburg, Ft. Wayne & Chicago Railroad. |
| Tablet | Pittsburg, Cincinnati & St. Louis Railroad. |
| Tactics | Pan Handle Railroad. |
| Tactile | Pennsylvania Central Railroad. |
| Tadpole | Union Pacific Railroad. |
| Taking | Vermont Central Railroad. |
| Supercede | Atchison, Topeka & Santa Fe. |
| Suppose | Boston & Albany. |
| Supposing | Boston & Maine. |
| Supreme | Burlington, Cedar Rapids & Northern. |
| Supremely | Burlington Route. |
| Surety | Canadian Pacific. |
| Surf | Chicago, Milwaukee & St. Paul. |
| Surface | Chicago, St. Paul, Minneapolis & Omaha. |
| Surfeit | Chicago, Indianapolis & Louisville. |
| Surfeiting | Chicago & Great Western. |
| Surgeful | Chicago & West Michigan. |
| Surgeon | Chicago & Eastern Illinois. |
| Surgery | Chicago & Erie. |
| Surgical | Chicago & Grand Trunk. |
| Surloin | Chicago, Hamilton & Dayton. |
| Surmise | Chicago Terminal Transfer. |
| Surpass | Chicago, Hammond & Western. |
| Surpassed | Chicago, Lake Shore & Eastern. |
| Surpassing | Chicago & Western Indiana. |
| Surplice | Cotton Belt Route. |
| Surplus | Cincinnati, New Orleans & Texas Pacific. |
| Surprisal | Cleveland, Belt & Terminal. |
| Surprised | Cleveland, Cincinnati, Chicago & St. Louis. |
| Surprising | Delaware, Lackawanna & Western. |
| Surrender | Delaware & Hudson. |
| Surrendered | Denver & Rio Grande. |
| Surrounding | Duluth, South Shore & Atlantic. |
| Survey | Elgin, Joliet & Eastern. |
| Surveyed | Fitchburg. |
| Surveying | Flint & Pere Marquette. |
| Surveyor | Grand Rapids & Indiana. |
| Survive | Great Northern. |
| Survival | Indiana, Illinois & Iowa. |
| Surviving | Iowa Central. |
| Suspect | Kansas City, Pittsburg & Gulf. |
| Suspecting | Kewaunee, Green Bay & Western. |
| Suspense | Lake Erie & Western. |
| Suspicion | Lehigh Valley. |
| Sustenance | Louisville & Nashville. |
| Swab | Maine Central. |
| Swabbed | Memphis Route. |
| Swabbing | Minneapolis & St. Louis. |
| Swarm | Minneapolis, St. Paul & Sault Ste. Marie. |
| Sweep | Missouri, Kansas & Texas. |
| Sweetened | Missouri Pacific. |
| Swelter | Mobile & Ohio. |
| Sweltered | Nashville, Chattanooga & St. Louis. |
| Sweltering | New York, Chicago & St. Louis. |
| Swipe | New York, New Haven & Hartford. |
| Swivel | New York, Ontario & Western. |
| Swoon | Ohio Central. |
| Swooning | Northern Pacific. |
| Swooped | Omaha & St. Louis. |
| Sword | Philadelphia & Reading. |
| Symbolism | Plant System. |
| Symbolize | Rome, Watertown & Ogdensburg. |
| Symmetry | Southern Railway. |
| Symphony | Southern Pacific. |
| Syncopist | St. Louis Southwestern. |
| Synodic | St. Louis & San Francisco. |
| Synopsis | Toledo, Ann Arbor & North Michigan. |
| Synoptic | Texas & Pacific. |
| Tabaret | Toledo, St. Louis & Kansas City. |
| Tabby | Texas Central. |
| Tabernacle | Union Pacific, Denver & Gulf. |
| Tabling | Vandalia Line. |
| Taboo | Wabash. |
| Tabular | West Shore. |
| Tabulate | Wisconsin Central. |
