In*ject"or (?), n. 1. One who, or that which, injects.

2. (Mach.) A contrivance for forcing feed water into a steam boiler by the direct action of the steam upon the water. The water is driven into the boiler by the impulse of a jet of the steam which becomes condensed as soon as it strikes the stream of cold water it impels; -- also called Giffard's injector, from the inventor.