Merriam-Webster Logo
SINCE 1828
Menu
dictionary thesaurus

si

noun
\ ˈsē How to pronounce si (audio) \

Definition of si

 (Entry 1 of 3)

: ti entry 1

Si

symbol

Definition of Si (Entry 2 of 3)

silicon

SI

abbreviation

Definition of SI (Entry 3 of 3)

International System of Units

First Known Use of si

Noun

1728, in the meaning defined above

History and Etymology for si

Noun

Italian

Abbreviation

French Système International d'Unités

Keep scrolling for more

Learn More about si

Dictionary Entries near si

shyster

SI

Si

si

Sia

siafu

sial

Statistics for si

Look-up Popularity

Time Traveler for si

The first known use of si was in 1728

See more words from the same year

Keep scrolling for more

More Definitions for si

Si

symbol

Medical Definition of Si

 (Entry 1 of 2)

silicon

SI

abbreviation

Medical Definition of SI (Entry 2 of 2)

International System of Units

History and Etymology for si

Abbreviation

French Système International d'Unités

More from Merriam-Webster on si

Rhyming Dictionary: Words that rhyme with si

Spanish Central: Translation of si

Comments on si

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

Show Comments  Hide Comments 

WORD OF THE DAY

pungle

Listen to the pronounciation of pungle

to make a payment or contribution

Get Word of the Day daily email!

Test Your Vocabulary

Time Traveler Quiz: Which Word Came First?

  • time traveler quiz which word came first
  • Which came first?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ
Word Winder's CrossWinder

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