Sed·​na ˈsed-nə How to pronounce Sedna (audio)
: a probable dwarf planet that orbits beyond the orbit of Neptune with a mean distance from the sun of about 520 astronomical units (48.3 billion miles)] and a diameter of approximately [870 miles (1400 kilometers)]
[The planetoid] Sedna at its closest approach to the sun is still two and half times as far away as Pluto. Its orbit will eventually take it more than 12 times that far away, into a dim exurb of the solar system where the sun looks more like an ordinary star.Joel Achenback, National Geographic, December 2004

Note: Sedna is believed to qualify as a dwarf planet under the current definition of that term, but precise identification of its characteristics is made difficult by its distance from the Earth.

Word History

First Known Use

2004, in the meaning defined above

Time Traveler
The first known use of Sedna was in 2004

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

  • More than 250,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!

Dictionary Entries Near Sedna

Cite this Entry

“Sedna.” Dictionary, Merriam-Webster, Accessed 18 Jul. 2024.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!