Sis and Si

Sis noun - A female person who has the same parents as another person.

Si is a synonym for sis. In some cases you can use "Si" instead a noun "Sis".

Si noun - 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.

Sis is a synonym for si. Sometimes you can replace term "Sis" with "Si", this nouns are similar.