Never mind the self-propelled cannon in a turret, mounted on all-terrian tracks that is the chief weapon in many of the world’s standing armies, nor even the metal or plastic storage vessels built to contain various types of liquid.
In rural Texas, parts of Oklahoma and a few other regions, a "tank" is a man-made pond with an earthen dam to store water for livestock use, home water supply and recreation.
Down here there is little standing water and subterranean aquifers are not present everywhere.
"Sometimes it rains and sometimes it doesn't," is an old homily that is only broken by the occasional torrential rain that fills the creek beds and makes the rivers run bank to bank over what was previously nothing more than parched sand.
Tanks are a partial answer to that infrequency problem we have with rain.
I don’t know when the first tank was dug or why the heck it got named a "tank." But the first ones were painstakingly dug by horse and mule teams which could only move several hundred pounds of dirt at a time.
They simply chose a wash or dry creek bed and piled dirt into a dam and trapped water behind the dam. Soil science was in its infancy but it was soon noticed that some dams held and some didn’t, due to the nature of the soil from which the dam was made. Clay soils made the best dams.
Later 20th century technology with its bulldozers, scrapers and transits enabled tank building to dig deeper and pile dirt higher until some property owners had mini reservoirs on their property, to the point of hindering water flow downstream.
Nowadays one cannot divert the flow by building tank dams that impede the natural flow of water. A deep hole is dug, and the dam has no role in diverting natural flow. The overflow or spillway is designed so that once the tank is full the excess water returns to its natural and original stream bed.
Besides their utilitarian properties of storing stock water, tanks have other functions. Many West Texas kids learn how to swim in them, learning to coexist with the turtles, snakes and frogs that also call their sometimes murky waters home.
Some of us learned it was best to leave encounters with these crawling neighbors out of conversations with our mothers.
Also, tanks could be stocked with fish and many a dry-lander has caught record-sized fish out of tanks.
So when we speak of tanks we are visioning a cool wet refuge in a parched land -- for cow and man alike.