1. n. [Drilling]

The structure used to support the crown blocks and the drillstring of a drilling rig. Derricks are usually pyramidal in shape, and offer a good strength-to-weight ratio. If the derrick design does not allow it to be moved easily in one piece, special ironworkers must assemble them piece by piece, and in some cases disassemble them if they are to be moved.

See: crown block,  derrickman,  escape line,  fingerboard,  gooseneck,  mast,  round trip,  sheave,  slide,  standpipe,  sub,  tongs,  traveling block