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• si
  si

  noun

  the syllable used for the seventh tone of a scale and sometimes for the tone B.
• Si
  Si

  silicon.
• SI
  SI

  abbreviation

  International System of Units.
• S.I.
  S.I.

  abbreviation

  Sandwich Islands.

si

¹ American  

[see] / si /

noun

Music.

1. the syllable used for the seventh tone of a scale and sometimes for the tone B.

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Si ² American  

Symbol, Chemistry.

1. silicon.

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SI ³ American  

abbreviation

1. International System of Units.

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S.I. ⁴ American  

abbreviation

1. Sandwich Islands.

2. Staten Island.

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SI ¹ British  

symbol

1. Système International (d'Unités) See SI unit

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abbreviation

1. South Island

Si ² British  

/ ʃiː /

noun

1. a variant transliteration of the Chinese name for the Xi

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Si ³ British  

symbol

1. silicon

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si ⁴ British  

/ siː /

noun

1. music a variant of te

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si ⁵ British  

abbreviation

1. Slovenia

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Etymology

Origin of si

First recorded in 1720–30; see origin at gamut

Example Sentences

To test the theory, Fang and Si conducted laboratory experiments using a thin layer of water driven by electromagnetic forces.

From Science Daily • Jun. 3, 2026

While Si was tied to the glitz and glamour of magazine business Condé Nast, Donald was a newspaper man at heart, known as a financially savvy publisher who respected his papers’ editorial independence.

From The Wall Street Journal • May 27, 2026

Together with his brother Samuel Irving Newhouse Jr., known as Si, Donald oversaw and expanded the sprawling media company that was founded by their father more than a century ago.

From The Wall Street Journal • May 27, 2026

Experts say "Magnifica Humanitas" could prove as influential as Pope Francis's "Laudato Si", a 2015 climate manifesto that triggered political and civic reactions worldwide.

From Barron's • May 25, 2026

Princess Si Ling-chi was sitting under a mulberry tree when a silkworm cocoon fell into her teacup.

From "Middlesex: A Novel" by Jeffrey Eugenides