at·​to- | \ˈa-(ˌ)tō\

Definition of atto- 

: one quintillionth (10−18) part of attogram

History and Etymology for atto-

International Scientific Vocabulary, from Danish or Norwegian atten eighteen, from Old Norse āttjān; akin to Old English eahtatīene eighteen

Keep scrolling for more

Learn More about atto-

Dictionary Entries near atto-

Attleboro

Attlee

attn

atto-

attorn

attorney

attorney-at-law

Statistics for atto-

Look-up Popularity

More from Merriam-Webster on atto-

Britannica.com: Encyclopedia article about atto-

Comments on atto-

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

WORD OF THE DAY

to enclose within walls

Get Word of the Day daily email!

Test Your Vocabulary

Late Autumn 2018 Words of the Day Quiz

  • frosted-autumn-leaves
  • Which is a synonym of yahoo?
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!