Prefix · half / partially
Signals half or partial degree: semicircle, semifinal, semiconductor, semicolon.
Written by Bryan López, English teacher · Updated
Semi- comes from Latin "semi" (half) and signals that something is half of what the root describes, or that it sits between two extreme states: semicircle = half a circle; semifinal = the round before the final; semiconductor = a material that conducts electricity only partially (between a conductor and an insulator); semiformal = not fully formal.
Semi- appears widely: semiconductor (fundamental in electronics), semipermeable (allows some things through but not others), semiannual (every six months), semiautomatic (partially automatic), semiskilled (with partial skills). In every case, semi- signals an intermediate or incomplete state.
Attaches to nouns and adjectives. Identical in Spanish and English:
Pronunciation: /ˈsemi/ in American English (both "i" sounds short and clear); /ˈsemaɪ/ in British English (second "i" long). Identical in Spanish and English.
semi-/ˈsemi/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
"Semicolon" (;) is stronger than a comma but weaker than a full stop. It links two closely related independent clauses. A "colon" (:) introduces a list, explanation, or quotation. They are distinct marks with different uses.
"Semi-" comes from Latin and "demi-" from French, but both mean "half." In English, "demi-god" and "demitasse" use the French variant. "Semi-" is more productive in scientific English; "demi-" appears mainly in French loanwords.
A trick to remember it
Semi- = "half" or "partially": semicircle = half a circle, semifinal = the round before the final, semiconductor = partially conducting. Identical in Spanish and English. When you see semi- before a technical word, think "between two extremes" or "halfway toward."
Exercise 1 · Form the word
Exercise 2 · Pick the right one
"Silicon is the most widely used ___ material in the manufacture of electronic circuits today."
Exercise 3 · Pick the right one
What is the difference between "semiannual" and "biannual"?
The prefix semi- signals half or partial degree: semicircle, semifinal, semiconductor, semicolon. In Spanish it usually maps to semi-.
The prefix semi- is pronounced /ˈsemi/. For example, "semicircle".
"circle" becomes "semicircle". It is a typical example of the semi- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.