haust

The root haust comes from Latin haurīre, 'to draw out, to drain,' with the past-participle form haustum. The original picture is concrete: drawing water out of a well bucket by bucket until the well runs dry. To haurīre was to empty something by pulling its contents out.

In English this root lives almost entirely inside one word and its offspring: exhaust.

- ex- (out) + haust (draw) = exhaust: to draw something completely out until nothing is left

From that single verb, the whole family grows by ordinary suffixes:

- exhausted: drawn completely empty of energy — what you feel after a long day
- exhausting: causing that draining — a thing that empties you out
- exhaustion: the state of being drained, of energy or of resources
- exhaustive: having drawn out every last possibility — covering absolutely everything

Notice the two directions the meaning travels. One is about energy: if a well can be drained dry, so can a person — to exhaust yourself is to pump out every last drop of strength. The other is about completeness: an exhaustive search has 'drawn out' every possibility, leaving none unchecked. Same image of total emptying, applied to a tank of energy or to a list of options.

And there is a wonderfully literal modern member: the exhaust of a car or engine — the spent gases drawn out and expelled. That is haust at its most concrete: pulling the used-up air right out the pipe. Every haust word, in the end, is about draining something to the bottom.