\Lay shaft\, or Layshaft \Lay"shaft`\, n. (Mach.)
A secondary shaft, as in a sliding change gear for an
automobile; a cam shaft operated by a two-to-one gear in an
internal-combustion engine. It is generally a shaft moving
more or less independently of the other parts of a machine,
as, in some marine engines, a shaft, driven by a small
auxiliary engine, for independently operating the valves of
the main engine to insure uniform motion.