1. (

• silicon ,
• Si ,
• atomic_number_ ,

) 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 ;

2. (

• Systeme_International_d'Unites ,
• Systeme_International ,
• SI_system ,
• SI ,
• SI_unit ,
• International_System_of_Units ,
• International_System

) 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" ;

3. (

• ti ,
• te ,
• si

) the syllable naming the seventh (subtonic) note of any musical scale in solmization ;