In quantum mechanics and quantum field theory, the propagator gives the probability amplitude for a particle to travel from one place to another in a given time, or to travel with a certain energy and momentum. In Feynman diagrams, which calculate the rate of collisions in quantum field theory, virtual particles contribute their propagator to the ... Found on http://en.wikipedia.org/wiki/Propagator
Prop'a·ga`tor noun [ Latin : confer French propagateur .] One who propagates; one who continues or multiplies. Found on http://www.encyclo.co.uk/webster/P/174