(verb)
to exhaust or deprive someone/something of energy, strength, or spirit;
e.g. Such experiences drain people and make them feel tired.
(verb)
to cause a resource to be used up, lost, or wasted, especially energy or money, or to be thus used up or wasted;
e.g. These expenses will drain his savings.
(verb)
to flow out of or away from something, or to be felt less strongly as time passes;
e.g. The water is allowed to drain into the lake. They felt the sadness drain from them.
(noun)
a structure such as a pipe, tube, or channel that is used to carry excess fluid/liquid away or draw it off to prevent it from accumulating;
e.g. The drain in the sink is clogged, causing water to stand.
(noun)
something that causes a resource to be continually expended, resulting in it's being used up or wasted;
e.g. This project has been a drain on my time.