semi- comb. form repr. L. sēmi- (partly through F., It., etc. semi-) ‘half’, (less strictly) ‘partly’, ‘partially’, equiv. in meaning to DEMI- and HEMI-, but in much more extensive use. L. sēmi- corr. to Gr. hēmi-, Skr. sāmi, and OS. sām-, OHG. sāmi-, OE. sām- (as in sambærned half-burnt, samcwic ‘half-alive’, half-dead). Exx. are semibreve XVI, semicircle XVI (L. sēmicirculus), semicircular XV (late L. -circulāris). semicolon XVII, semiquaver XVI, semitone XVII (cf. late L. sēmitonium), semivowel XVI (L. sēmivocālis).

semi- • prefix 1. half: semicircular. ∎  occurring or appearing twice in a specified period: semiannual.2. partly; in some degree or particular: semiconscious. ∎  almost: semidarkness.

semi- prefix denoting half.