Originally a barrel-shaped bird net in Old French, 'tunnel' migrated underground when engineers borrowed the barrel-vault shape for subterranean passages.
An underground or underwater passage, typically one built through a hill or beneath a road, river, or building.
From Old French tonel, meaning 'cask' or 'barrel', a diminutive of tonne ('barrel'). The word originally referred to a barrel-shaped net used for catching birds or fish, and only later shifted to mean an underground passage — the shape of a barrel vault providing the semantic bridge. The Old French tonne itself derives from Medieval Latin tunna, a word of uncertain but possibly Celtic origin referring to a large cask. The architectural sense emerged in the 16th century as mining and civil