Big Huge Thesaurus

underground

adjective

• belowground
• clandestine
• cloak-and-dagger
• hugger-mugger
• hush-hush
• secret
• surreptitious
• undercover
• hole-and-corner

similar terms

• covert
• subsurface

noun

• resistance
• metro
• tube
• subway system
• subway
• railroad
• railroad line
• railway
• railway line
• railway system
• revolutionary group

sounds kind of like

• undercurrent
• undergarment

rhymes with

• background
• battleground
• campground
• earthbound
• eastbound
• fairground
• foreground
• foxhound
• greyhound
• hidebound
• homebound
• horehound
• merry-go-round
• outbound
• playground
• snowbound
• southbound
• spellbound
• westbound