A synecdoche is a more narrowly defined metonymy. While a metonymy substitues one concept for any concept associated with it, a synecdoche substitues a part for the whole or a whole for a part.  In the example of a "hired hand," hand is used in place of a whole person or worker. A material thing can also be used in place of the object from which it is made, as in steel for a sword.

An important synecdoche in scripture is "the blood of Christ." The actual physical blood of Jesus is gone and cannot be said to have any efficacious value. Instead the blood is a synecdoche standing for Christ's sacrificial death and triumphant resurrection. It is not the actual blood of Christ that saves, but his death and resurrection. We and the Biblical authors use the word blood (Eph. 2:13; Heb. 9:11) and in place of death and resurrection because those words are a graphic reminders of Christ's work and are more literarily interesting than continually describing the events. Similiarly, when Paul calls people, "enemies of the cross of Christ," the cross (1 Cor. 1:17; Gal. 6:12) is used in place of the whole Christian faith.