Source : Webster's Revised Unabridged Dictionary (1913)

Derrick \Der"rick\, n. (Mining)
   The pyramidal structure or tower over a deep drill hole, such
   as that of an oil well.

Derrick \Der"rick\, n. [Orig., a gallows, from a hangman named
   Derrick. The name is of Dutch origin; D. Diederik, Dierryk,
   prop. meaning, chief of the people; cf. AS. pe['o]dric, E.
   Theodoric, G. Dietrich. See {Dutch}, and {Rich}.]
   A mast, spar, or tall frame, supported at the top by stays or
   guys, with suitable tackle for hoisting heavy weights, as
   stones in building.

   {Derrick crane}, a combination of the derrick and the crane,
      having facility for hoisting and also for swinging the
      load horizontally.

Source : WordNet®

derrick
     n 1: a framework erected over an oil well to allow drill tubes to
          be raised and lowered
     2: a simple crane having lifting tackle slung from a boom