[ see ]

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

Origin of si

First recorded in 1720–30; see origin at gamut

Other definitions for Si (2 of 4)


Symbol, Chemistry.
  1. silicon.

Other definitions for SI (3 of 4)


Other definitions for S.I. (4 of 4)


  1. Sandwich Islands.

  2. Staten Island. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use si in a sentence

  • And here's a perfectly beautiful one D-i-o-n-y-s-i-u-s Carpenter.

    Tabitha at Ivy Hall | Ruth Alberta Brown
  • "Silence, s-i-l-e-n-c-e," gravely spelled Susie, while the whole meeting-house rang with the applause that greeted her.

    Winter Fun | William O. Stoddard
  • The seed of the s-i grass is also used for the same purpose, and is said to be a prophylactic against stomach troubles.

    The Manbos of Mindano | John M. Garvan
  • “T-h-e f-i-n-e-s-t s-i-l-k r-a-g-s,” he expostulated 95 again holding two fingers under the nose of Rags Habakuk.

    Rootabaga Stories | Carl Sandburg
  • Mr. S.-I think a lady should not write verses till she is past receiving them.

British Dictionary definitions for si (1 of 5)


/ (siː) /

  1. music a variant of te

British Dictionary definitions for si (2 of 5)


the internet domain name for
  1. Slovenia

British Dictionary definitions for Si (3 of 5)


Si Kiang

/ (ʃiː) /

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

British Dictionary definitions for Si (4 of 5)


the chemical symbol for
  1. silicon

British Dictionary definitions for SI (5 of 5)


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

abbreviation for
  1. NZ South Island

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for Si


The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.