Merriam-Webster Logo
SINCE 1828
Menu
dictionary thesaurus

Iapetus

noun
Iap·​e·​tus | \ ī-ˈa-pə-təs How to pronounce Iapetus (audio) \

Definition of Iapetus

astronomy
: the third largest satellite of Saturn with a diameter of approximately 890 miles (1440 km) Ever since J.D. Cassini discovered the object in 1671, astronomers have puzzled over why Iapetus' leading hemisphere (facing forward along its orbit) is dark and its trailing one bright.— J. Kelly Beatty, Sky & Telescope, November 1983

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!

Learn More about Iapetus

Dictionary Entries near Iapetus

ianthinite

iao

IAP

Iapetus

Iapygian

Iapygidae

iarovize

Statistics for Iapetus

Look-up Popularity

Comments on Iapetus

What made you want to look up Iapetus? Please tell us where you read or heard it (including the quote, if possible).

Show Comments  Hide Comments 

WORD OF THE DAY

contraption

Listen to the pronounciation of contraption

a device or gadget

Get Word of the Day daily email!

Test Your Vocabulary

Words for Summer: A Quiz

  • a closeup of a sunflower
  • Which of the following words means “of or relating to summer”?
True or False

Test your knowledge - and maybe learn something along the way.

TAKE THE QUIZ
Dictionary Devil

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ
Love words? Need even more definitions?

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

Words at Play
Ask the Editors
Word Games