si meaning and definition

SI noun

Definition of Si (noun)

1. 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
   • synonyms: atomic number 14, silicon
2. 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"
   • synonyms: International System, International System of Units, SI system, SI unit, Systeme International, Systeme International d'Unites
3. the syllable naming the seventh (subtonic) note of any musical scale in solmization
   • synonyms: te, ti