To lose liquid.
The clogged sink drained slowly.
To flow gradually.
The water of low ground drains off.
To cause liquid to flow out of.
Please drain the sink. It's full of dirty water.
To convert a perennially wet place into a dry one.
They had to drain the swampy land before the parking lot could be built.
To deplete of energy or resources.
The stress of this job is really draining me.
To draw off by degrees; to cause to flow gradually out or off; hence, to exhaust.
To filter.
To fall off the bottom of the playfield.
Lacking motivation and energy; very tired; knackered.
I felt so drained after that three-hour exam that I wanted to sleep for the next week.
Of a battery, empty of charge; discharged.