-si

from The Collaborative International Dictionary of English v.0.48

Si \Si\ [It.] (Mus.)
   A syllable applied, in solmization, to the note B; more
   recently, to the seventh tone of any major diatonic scale. It
   was added to Guido's scale by Le Maire about the end of the
   17th century.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Maffioso \Maf`fi*o"so\, Mafioso \Ma`fi*o"so\, n.; pl. {-si}.
   [It. maffioso.]
   A member of the mafia.
   [Webster 1913 Suppl.]

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

SI
       Schweizer Informatikergesellschaft (org., Switzerland)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

SI
       Skyrslutaeknifelags Islands (org., Iceland)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

SI
       Source Index [register] (CPU, Intel, assembler)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

SI
       SPARC International (org., manufacturer)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

SI
       System Identifier (DTD, URI, SGML, FPI)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

SI
       System Information