To channel (a stream of water) through a culvert.
A channel crossing under a road or railway for the draining of water.
To surround with a moat.
A clear ring outside the eyewall of a tropical cyclone.
An aspect of a business which makes it more "defensible" from competitors, because of the nature of its products, services or franchise or for some other reason.
A circular lowland between a resurgent dome and the walls of the caldera surrounding it.
A deep, wide defensive ditch, normally filled with water, surrounding a fortified habitation.