To save this word, you'll need to log in.
Iap·e·tus | \ ī-ˈa-pə-təs 
\
\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
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).
Test Your Vocabulary
More Confusing Words—Quiz
- The magician
______moved the selected card to the top of the deck.
Can you spell these 10 commonly misspelled words?
TAKE THE QUIZ
Test Your Knowledge - and learn some interesting things along the way.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridgedWords at Play
Ask the Editors
Word Games
- More Confusing Words—Quiz
How many of these commonly confused words do you know?
Take the quiz - Name that Thing: Toys and Games Edition
It's all fun and games until someone beats your high score.
Take the quiz - Spell It
Can you spell these 10 commonly misspelled words?
Take the quiz - Citation
Do you know the person or title these quotes describe?
Play the game
Share Iapetus