Tunnel  —n. 1 underground passage dug through a hill or under a road, river, etc., esp. For a railway or road. 2 underground passage dug by an animal. —v. (-ll-; us -l-) 1 (foll. By through, into, etc.) Make a tunnel through. 2 make (one's way) by tunnelling. [french diminutive of tonne *tun]