Si vs Ssu

Si

name

  • A diminutive of the male given name Simon. 

  • A river in Shandong, China. 

  • Various prefectures of imperial China. 

  • A diminutive of the male given name Silas. 

  • A county in Anhui, China. 

Ssu

How often have the words Si and Ssu occurred in a corpus of books? (source: Google Ngram Viewer )