Pluto

As a proper noun referring to a specific celestial body or a specific deity, this word is used exclusively in the singular. It does not take a plural form in standard usage.

In astronomical contexts, the term is often associated with the debate over planetary classification, frequently appearing alongside terms like dwarf planet or Kuiper belt. In mythological contexts, it is used to denote the Roman personification of the underworld, often contrasted with Jupiter or Neptune.