What does Si mean?
(male) Sei, Sin, ..
(female) Se, Sli, ..
How popular is Si?
Si is an uncommon first name for males but a very popular last name for all people (#32743 out of 150436, Top 22%). (2000 U.S. Demographics)
Simon (#231 from current records) and Sim are the popular varying forms of Si (not in Top 2000) listed in the Top 2000. Adoption of these forms of Si was at its highest in the 1880s (adoption of 0.1%) and is almost as conventional today (adoption 0.08%, 11.4% less), but with the version Sim becoming somewhat outmoded. Simon is the most fashionable name for newborns in this list. Below is a graphed comparison of the usage of Si and related names. (2014 Birth Statistics)