solenoid
    n 1: a coil of wire around an iron core; becomes a magnet when
         current passes through the coil

Solenoid \So"len*oid\, n.[Gr. ??? channel + -oid.] (Elec.)
   An electrodynamic spiral having the conjuctive wire turned
   back along its axis, so as to neutralize that component of
   the effect of the current which is due to the length of the
   spiral, and reduce the whole effect to that of a series of
   equal and parallel circular currents. When traversed by a
   current the solenoid exhibits polarity and attraction or
   repulsion, like a magnet.
   [1913 Webster]