SIabbr. French Système International [d’Unités] (International System [of Units])Si 1The symbol for silicon.Si 2abbr. Bible Sirachsi (s?)n. Music Ti.[Italian, from Medieval Latin; see gamut.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.si (si?) n (Classical Music) music a variant of tesi the internet domain name for (Computer Science) Slovenia Si (?i?) or Si Kiangn (Placename) a variant transliteration of the Chinese name for the XiSi the chemical symbol for (Elements & Compounds) silicon SI symbol for (Units) Système International (d’Unités). See SI unit abbreviation for (Placename) NZ South Island Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014SI International System of Units. [