What does the prefix semi- mean?
Semi- comes from the Latin semi, which means "half". It shows that something is half of what the base word says, or that it is at a middle point between two extremes.
ESEN
Prefix · half / partially
semi-
Signals half or partial degree: semicircle, semifinal, semiconductor, semicolon.
Scientific
Written by Bryan López, English teacher · Updated
Semi- in science and daily life
Semi- appears in many contexts with the same idea of "halfway". In electronics, it names materials that conduct electricity only partly. In daily life, it talks about something that repeats every six months or that works in a partially automatic way. When you see semi-, think of an intermediate or incomplete state.
How it is used
Attaches to nouns and adjectives:
- semi- + geometric/mathematical nouncircle → semicirclefinal → semifinalcolon → semicolonsphere → hemisphere
- semi- + technical adjective/nounconductor → semiconductorpermeable → semipermeableautomatic → semiautomaticannual → semiannual
Pronunciation: /ˈsemi/ in American English (both "i" sounds short and clear); /ˈsemaɪ/ in British English (second "i" long).
How it is pronounced
semi-/ˈsemi/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With semi-
In a phrase
- circlesemicircleThe students arranged their chairs in a semicircle.
- finalsemifinalThey beat the top team in the semifinal and reached the final.
- colonsemicolonA semicolon connects two closely related independent clauses.
- conductorsemiconductorSilicon is the most widely used semiconductor material.
- automaticsemiautomaticThe machine is semiautomatic and still needs an operator to start it.
- annualsemiannualThe company publishes a semiannual report each June and December.
- permeablesemipermeableCell membranes are semipermeable, letting some molecules through but not others.
Common mistakes
semicolon = colon (both are punctuation)
semicolon (;) = point and comma; colon (:) = double point — they are different marks
"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- and demi- are completely different
semi- (Latin) and demi- (French) mean the same thing: half
"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. When you see semi- before a technical word, think "between two extremes" or "halfway toward."
Practise what you learned
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"?
Frequently asked questions
What does the prefix semi- mean in English?
The prefix semi- signals half or partial degree: semicircle, semifinal, semiconductor, semicolon.
How do you pronounce semi-?
The prefix semi- is pronounced /ˈsemi/. For example, "semicircle".
Can you give an example of a word with semi-?
"circle" becomes "semicircle". It is a typical example of the semi- prefix.
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