Noun
1. (astronomy) an indistinct surface feature of Mars once thought to be a system of channels; they are now believed to be an optical illusion
2. a bodily passage or tube lined with epithelial cells and conveying a secretion or other substance;
"the tear duct was obstructed""the alimentary canal""poison is released through a channel in the snake's fangs"3. long and narrow strip of water made for boats or for irrigation