Tunnel/ˈtʌnl/ Definition 1 of 4Pro Tip 1/3Physical Structures Used to describe structures allowing transportation through obstacles. The new tunnel connects two major cities. Pro Tip 2/3Metaphorical Use Sometimes 'tunnel' may represent a challenge or journey in life. He's going through a dark tunnel, but he'll emerge stronger. Pro Tip 3/3Not Always Underground Tunnels can be above ground, like wildlife crossings over highways. The wildlife tunnel helps animals cross safely.