Gabor Klima tunnel tun⋅nel [tuhn-l] –noun 1. an underground passage. 2. a passageway, as for trains or automobiles, through or under an obstruction, as a city, mountain, river, harbor, or the like. 3. an approximately horizontal gallery or corridor in a mine. 4. the burrow of an animal. home t a b c d e f g h i j k l m n o p q r s t u v w x y z tunnel twin