a dead body: the lifeless corpse of an animal or person, treated as unclean
This word names a dead body, but with a sharp edge the plain word "corpse" misses: it is a body that is defiling to touch. In Israel's law a corpse is the most powerful source of ritual uncleanness, and this is the word for it. So the term carries not just death but contamination, and the danger of spreading that contamination to anyone who handles it or eats it.
The same word covers the carcass of an animal and the corpse of a person, because the issue is the same in both: lifeless flesh that the living must keep away from. With animals it usually means one that died on its own or was torn, never properly slaughtered, which is exactly why it is unfit to eat. With people it most often appears in scenes of judgment, where a body is left lying in the open, unburied, as the ultimate disgrace.
From there the word stretches one step further. The prophet Jeremiah calls Israel's idols by this very name: lifeless things, as dead and defiling as a corpse. It is a deliberate insult, branding the gods people trusted as nothing more than dead flesh.