Semi- \Sem"i-\ [L. semi; akin to Gr. ???, Skr. s[=a]mi-, AS. s[=a]m-, and prob. to E. same, from the division into two parts of the same size. Cf. Hemi-, Sandelend.]

A prefix signifying half, and sometimes partly or imperfectly; as, semiannual, half yearly; semitransparent, imperfectly transparent.

Note: The prefix semi is joined to another word either with the hyphen or without it. In this book the hyphen is omitted except before a capital letter; as, semiacid, semiaquatic, semi-Arian, semiaxis, semicalcareous.

Source: Webster's Revised Unabridged Dictionary (1913)