Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

SI
     n 1: a complete metric system of units of measurement for
          scientists; fundamental quantities are length (meter)
          and mass (kilogram) and time (second) and electric
          current (ampere) and temperature (kelvin) and amount of
          matter (mole) and luminous intensity (candela); "Today
          the United States is the only country in the world not
          totally committed to the Systeme International d'Unites"
          [syn: {Systeme International d'Unites}, {Systeme
          International}, {SI system}, {International System of
          Units}, {International System}]
     2: a tetravalent nonmetallic element; next to oxygen it is the
        most abundant element in the earth's crust; occurs in clay
        and feldspar and granite and quartz and sand; used as a
        semiconductor in transistors [syn: {silicon}, {atomic
        number 14}]
     3: the syllable naming the seventh (subtonic) note of any
        musical scale in solmization [syn: {ti}, {te}]

Source : Free On-Line Dictionary of Computing

si
     
         The {country code} for Slovenia.
     
        (1999-01-27)