One who initiates.
A substance that initiates a chain reaction or polymerization.
A component of a nuclear weapon that produces a burst of neutrons to trigger a fission chain reaction.
A task (in a mainframe computer) that initiates multiple jobs.
A material whose presence in the body eventually leads to cancer.
One who shapes.
A machine tool in which a single-point cutting tool mounted on a reciprocating ram is traversed across the workpiece linearly. Shapers can generate various shapes, but were most especially employed in generating flat surfaces and keyways. The shaper is nowadays obsolescent, most of its applications being served by milling machines.
A person who designs and builds surfboards.