rocking shaft

from The Collaborative International Dictionary of English v.0.48

Rock shaft \Rock" shaft`\ [Cf. {Rock}, v. i.] (Mach.)
   A shaft that oscillates on its journals, instead of
   revolving, -- usually carrying levers by means of which it
   receives and communicates reciprocating motion, as in the
   valve gear of some steam engines; -- called also {rocker},
   {rocking shaft}, and {way shaft}.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Rocking \Rock"ing\, a.
   Having a swaying, rolling, or back-and-forth movement; used
   for rocking.
   [1913 Webster]

   {Rocking shaft}. (Mach.) See {Rock shaft}.
      [1913 Webster]