tunnel
n. countablen. a long passage that goes under the ground, through a mountain, or under a river. You use it to travel from one side to the other by car, train, or on foot.
n. an artificial underground passage, typically bored through earth or rock, to allow for the transit of vehicles, pedestrians, or utilities.
The train goes through a long tunnel under the mountain.
Engineers are building a new tunnel to connect the two islands and reduce travel time for commuters.
The construction of the subaqueous tunnel required advanced boring machines capable of maintaining structural integrity against the immense pressure of the overlying seabed.
From Middle French tonnelle (“net”) or tonel (“cask”), diminutive of Old French tonne (“cask”), a word of uncertain origin and affiliation. Related to Old English tunne (“tun; cask; barrel”). More at tun.
Often used with the prepositions 'through' or 'under'.