semi

noun Informal.

1. semitrailer(def 1).
2. Often semis. semifinal(def 3).

1. a combining form borrowed from Latin, meaning “half,” freely prefixed to English words of any origin, now sometimes with the senses “partially,” “incompletely,” “somewhat”: semiautomatic; semidetached; semimonthly; semisophisticated.

noun plural semis

1. British a semidetached house
2. short for semifinal
3. US, Canadian, Australian and NZ short for semitrailer

prefix

1. halfsemicircle Compare demi- (def. 1), hemi-
2. partially, partly, not completely, or almostsemiprofessional; semifinal
3. occurring twice in a specified period of timesemiannual; semiweekly

before vowels sem-, word-forming element meaning “half, part, partly; partial, imperfect; twice,” from Latin semi- “half,” from PIE *semi- “half” (cf. Sanskrit sami “half,” Greek hemi- “half,” Old English sam-, Gothic sami- “half”). Old English cognate sam- was used in such compounds as samhal “poor health,” literally “half-whole;” samsoden “half-cooked,” figuratively “stupid” (cf. half-baked); samcucu “half-dead,” literally “half-alive;” and the last survivor of the group, sandblind “dim-sighted” (q.v.). Common in Latin (e.g. semi-gravis “half-drunk,” semi-hora “half hour,” semi-mortuus “half-dead,” semi-nudus “half-naked,” semi-vir “half-man, hermaphrodite”). The Latin-derived form in English has been active in forming native words since 15c. pref.

1. Half:semicanal.
2. Partial; partially:semiconscious.
3. Resembling or having some of the characteristics of:semilunar.

1. A prefix that means “half,” (as in semicircle, half a circle) or “partly, somewhat, less than fully,” (as in semiconscious, partly conscious).