canal

(noun) (astronomy) an indistinct surface feature of Mars once thought to be a system of channels; they are now believed to be an optical illusion.

(noun) a bodily passage or tube lined with epithelial cells and conveying a secretion or other substance. Synonyms: duct, epithelial duct, channel. Examples: "The tear duct was obstructed." "The alimentary canal." "Poison is released through a channel in the snake's fangs."

(noun) long and narrow strip of water made for boats or for irrigation.

(verb) provide (a city) with a canal. Synonyms: canalize, canalise.