Semi- (?). [L. semi; akin to Gr. &unr_;&unr_;&unr_;, Skr. sāmi-, AS. sām-, 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.
[1913 Webster]

&hand_; 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.
[1913 Webster]