Definitions from Wiktionary ( )

▸ noun:  An underground or underwater passage.
▸ noun:  A passage through or under some obstacle.
▸ noun:  A hole in the ground made by an animal, a burrow.
▸ noun:  (computing, networking) A wrapper for a protocol that cannot otherwise be used because it is unsupported, blocked, or insecure.
▸ noun:  A vessel with a broad mouth at one end, a pipe or tube at the other, for conveying liquor, fluids, etc., into casks, bottles, or other vessels; a funnel.
▸ noun:  The opening of a chimney for the passage of smoke; a flue.
▸ noun:  (mining) A level passage driven across the measures, or at right angles to veins which it is desired to reach; distinguished from the drift, or gangway, which is led along the vein when reached by the tunnel.
▸ noun:  (figurative) Anything that resembles a tunnel.
▸ verb:  (transitive) To make a tunnel through or under something; to burrow.
▸ verb:  (intransitive) To dig a tunnel.
▸ verb:  (computing, networking) To transmit something through a tunnel (wrapper for an insecure or unsupported protocol).
▸ verb:  (transitive, medicine) To insert a catheter into a vein to allow long-term use.
▸ verb:  (physics) To undergo the quantum-mechanical phenomenon where a particle penetrates through a barrier that it classically cannot surmount.

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