The trachea.
A flight path used by aeroplanes.
a vessel for conveying lymph or glandular secretions such as tears or bile
a tube or elongated cavity (such as a xylem vessel) for conveying water, sap, or air
a pipe, tube or canal which carries gas or liquid from one place to another
a layer (as in the atmosphere or the ocean) which occurs under usually abnormal conditions and in which radio or sound waves are confined to a restricted path
an enclosure or channel for electrical cable runs, telephone cables, or other conductors
to enclose in a duct
to channel something (such as a gas) or propagate something (such as radio waves) through a duct or series of ducts