Meaning

noun a nonenterprising person who is not paying his way

noun a train or bus or taxi traveling empty

originFrom dead + head. Some senses are derived from theater jargon (originally spelled dead head) for audience members admitted without paying, which probably arose in analogy to dead weight or deadwood in reference to their lack of contribution to revenue or in reference to their unenthusiastic (dead) response to performances. Perhaps even from Latin caput mortuum, alchemy term for distillation…

Etymology from Wiktionary, CC BY-SA 3.0