Si, SI or si may refer to: Si (novel), a 2014 novel by Bob Ong. Sí (Peruvian magazine), a magazine notable for its anti-corruption reporting.

Sports Illustrated, SI.com provides sports news, expert analysis, highlights, stats and scores for the NFL, NBA, MLB, NHL, college football, soccer, fantasy, gambling and more.

Acronym of Latin Sancte Ioannes, the phrase ending the hymn Ut queant laxis from earlier words of which the other notes of solfège were derived. IPA(key): /si/. si (plural sis). (music) A syllable used in solfège to represent the seventh note of a major scale.

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The International System of Units (abbreviated SI from the French language name Système International d'Unités ) is the modern form of the metric system . It is the world's most widely used system of units , both in everyday commerce and in science .