subway (n.)

• branch
• bunker
• burrow
• cave
• cavern
• choo-choo
• cove
• dugout
• el
• electric
• elevated
• embankment
• express
• feeder
• flier
• foxhole
• freight
• freighter
• funicular
• grot
• grotto
• hole
• junction
• lair
• limited
• line
• local
• metro
• monorail
• rail
• railroad
• railway
• rattler
• roadbed
• roadway
• sewer
• shuttle
• sidetrack
• siding
• special
• streamliner
• terminal
• terminus
• track
• train
• tram
• tramline
• trestle
• trunk
• tube
• tunnel
• turnout
• underground
• underpass
• warren