The Collaborative International Dictionary of English v.0.48:

Drain \Drain\ (dr[=a]n), v. t. [imp. & p. p. Drained
   (dr[=a]nd); p. pr. & vb. n. Draining.] [AS. drehnigean to
   drain, strain; perh. akin to E. draw.]
   1. To draw off by degrees; to cause to flow gradually out or
      off; hence, to cause the exhaustion of.
      [1913 Webster]

            Fountains drain the water from the ground adjacent.
                                                  --Bacon.
      [1913 Webster]

            But it was not alone that the he drained their
            treasure and hampered their industry. --Motley.
      [1913 Webster]

   2. To exhaust of liquid contents by drawing them off; to make
      gradually dry or empty; to remove surface water, as from
      streets, by gutters, etc.; to deprive of moisture; hence,
      to exhaust; to empty of wealth, resources, or the like;
      as, to drain a country of its specie.
      [1913 Webster]

            Sinking waters, the firm land to drain,
            Filled the capacious deep and formed the main.
                                                  --Roscommon.
      [1913 Webster]

   3. To filter.
      [1913 Webster]

            Salt water, drained through twenty vessels of earth,
            hath become fresh.                    --Bacon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Drain \Drain\, v. i.
   1. To flow gradually; as, the water of low ground drains off.
      [1913 Webster]

   2. To become emptied of liquor by flowing or dropping; as,
      let the vessel stand and drain.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Drain \Drain\, n.
   1. The act of draining, or of drawing off; gradual and
      continuous outflow or withdrawal; as, the drain of specie
      from a country; the project is a drain on resources.
      [1913 Webster]

   2. That means of which anything is drained; a channel; a
      trench; a water course; a sewer; a sink.
      [1913 Webster]

   3. pl. The grain from the mashing tub; as, brewers' drains.
      [Eng.] --Halliwell.
      [1913 Webster]

   Box drain, Counter drain. See under Box, Counter.

   Right of drain (Law), an easement or servitude by which one
      man has a right to convey water in pipes through or over
      the estate of another. --Kent.
      [1913 Webster]

WordNet (r) 3.0 (2006):

drain
    n 1: emptying something accomplished by allowing liquid to run
         out of it [syn: drain, drainage]
    2: tube inserted into a body cavity (as during surgery) to
       remove unwanted material
    3: a pipe through which liquid is carried away [syn: drain,
       drainpipe, waste pipe]
    4: a gradual depletion of energy or resources; "a drain on
       resources"; "a drain of young talent by emigration"
    v 1: flow off gradually; "The rain water drains into this big
         vat" [syn: drain, run out]
    2: deplete of resources; "The exercise class drains me of
       energy"
    3: empty of liquid; drain the liquid from; "We drained the oil
       tank"
    4: make weak; "Life in the camp drained him" [syn: enfeeble,
       debilitate, drain]

The Free On-line Dictionary of Computing (19 January 2023):

drain

    (IBM) To allow a system to complete the processing of
   its current work before the system becomes unavailable.
   E.g. draining a device before taking it off-line or telling
   a web server in a server farm not to accept any new
   requests but to finish processing any requests it has already
   accepted.

   [Jargon File]

   (2005-07-18)


The Jargon File (version 4.4.7, 29 Dec 2003):

drain
 v.

    [IBM] Syn. for flush (sense 2). Has a connotation of finality about it;
    one speaks of draining a device before taking it offline.