Source : Webster's Revised Unabridged Dictionary (1913)

Screw \Screw\, v. t. [imp. & p. p. {Screwed}; p. pr. & vb. n.
   {Screwing}.]
   1. To turn, as a screw; to apply a screw to; to press,
      fasten, or make firm, by means of a screw or screws; as,
      to screw a lock on a door; to screw a press.

   2. To force; to squeeze; to press, as by screws.

            But screw your courage to the sticking place, And
            we'll not fail.                       --Shak.

   3. Hence: To practice extortion upon; to oppress by
      unreasonable or extortionate exactions.

            Our country landlords, by unmeasurable screwing and
            racking their tenants, have already reduced the
            miserable people to a worse condition than the
            peasants in France.                   --swift.

   4. To twist; to distort; as, to screw his visage.

            He screwed his face into a hardened smile. --Dryden.

   5. To examine rigidly, as a student; to subject to a severe
      examination. [Cant, American Colleges]

   {To screw out}, to press out; to extort.

   {To screw up}, to force; to bring by violent pressure.
      --Howell.

Screwing \Screw"ing\,
   a. & n. from {Screw}, v. t.

   {Screwing machine}. See {Screw machine}, under {Screw}.

Source : WordNet®

screwing
     n : slang terms for sexual intercourse [syn: {fuck}, {fucking},
         {screw}, {ass}, {nooky}, {nookie}, {piece of ass}, {piece
         of tail}, {roll in the hay}, {shag}, {shtup}]