| Word | Definitions | Synonyms |
|---|---|---|
| subway | (noun) an electric railway operating below the surface of the ground (usually in a city) | Synonyms: metro, subway system, tube, underground |
| (noun) an underground tunnel or passage enabling pedestrians to cross a road or railway | Synonyms: underpass | |
| subwoofer | (noun) a loudspeaker that is designed to reproduce very low bass frequencies | - |