What is the difference between the root "hemi", the root "semi", and the root "demi"? For instance, one would say "hemisphere" or "semicircle" but one wouldn't say "Hemicircle". (I know one is Greek and one is Latin.) What are the rules for using them? Also, is semisphere correct?

  • 14
    Let's not demote demi as a contender. Nov 9 at 16:15
  • 3
    Nor half- for that matter.
    – fev
    Nov 9 at 16:20
  • 3
    The usual rule, dn – do what most consider normal, which leads to the minimum amount of confusion. Dictionaries list common usages. The hemidemisemiquaver or semidemisemiquaver ('British English') shows that usage is at best not very logical (why not demihemisemi ...?) Nov 9 at 16:34
  • 11
    Fun fact: hemidemisemiquaver is a term used in music for a 1/64th-length note (a "quaver" being a 1/8 note, then halved three times). So they're not exclusive (and yet you wouldn't reorder those prefixes).
    – Miral
    Nov 10 at 0:40
  • 4
    I'm casting my vote to reopen it because the answers posted here are original and fruit of users' knowledge and expertise. Not copied verbatim from Quora. I have nothing against the website but answers that are copied should be formatted in such a way to make this clearer. The answer posted in the older question is practically a screenshot.
    – Mari-Lou A
    Nov 10 at 10:36

5 Answers 5


The three prefixes originally had overlap but some different nuances:

"semi-" was used generally and imprecisely: it did mean "half" but with some latitude.

"demi" was used to mean half of a figure/body and also "not quite a [noun]"

hemi- was used for half of a symmetrical object around the line of symmetry. It was more popular in technical terms.


Semi- prefix:

Etymology: representing Latin sēmi- ... = Sanskrit sāmi- , Greek ἡμι- , Old High German sâmi- , Old Saxon sâm- , cognate with Old English sam-

Demi (adj and noun) Etymology: < French demi < Latin dīmidium half: see dimidiate adj. The French word is a noun and adjective, and much used in combination. It began to be used in English in the 15th cent. attributive in Heraldry, and in the 16th cent. in names of cannon, and soon passed to other uses.

  1. In general use.

a. (a) Compounded with adjectives and participles, with the meaning ‘half, partly, partially, to some extent’. A few are used elliptically as nouns.

1871 W. Bagehot in Fortn. Rev. 1 Aug. 158 A semi-abstract discussion of practical topics.

demi-, prefix

Etymology: < demi adj. and n.

Used with the senses ‘half, half-sized, partial(ly), curtailed, inferior’.

  1. In Heraldry, etc., indicating the half-length figure of a person or animal, or the half of a charge or bearing. 1486 Bk. St. Albans, Her. B v a Demy is calde in armys halfe a best in the felde.

hemi-, prefix

Etymology: < Greek ἡμι-, combining form, from earlier *σᾱμι- = Latin sēmi- , Sanskrit sāmi- , Old Germanic *sâmi- ,...Several Greek words containing this element were in use as technical terms in later Latin, e.g. hēmicyclium , hēmīna , hēmisphærium , hēmistichium . In the modern languages they are very numerous, not only in terms adopted or adapted < Greek (directly or through Latin), but in new formations, scientific or technical, < Greek, or on Greek analogies. Words formed < Latin have the corresponding prefix semi- prefix; but there are instances of hybridism in the use of both prefixes.

  1. Half-; one half, the half, pertaining to or affecting one half; esp. in Anatomy, Biology, and Pathology. Pertaining to one of the two halves (right and left) of the body, or of any of its symmetrical organs.

The infrequent use of these prefixes, their similar applications and sounds, and a general lazy tendency of language to gravitate towards a mean has caused all three to be used either as they were fossilised, or to be used to create words that "sound authentic".

  • What was the need to provide this lengthy answer, when you could have pointed OP and other visitors to this answered question "Demi-,semi-,hemi- Usage with words" @ english.stackexchange.com/questions/356565/…?
    – banuyayi
    Nov 10 at 5:08
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    @banuyayi So why did you post an answer that is basically a rehash of Tum's excellent one? Why didn't you post your new answer on the older question? Maybe Greybeard didn't know a very similar question had been posted and answered before. In any case, Greybeard's answer is original, and adds details by citing an authoritative reference.
    – Mari-Lou A
    Nov 10 at 9:25
  • My comment was not intended to give rise to rancor. I have debated and posted my answer as an answer. Many people do not read comments, read only answers. My answer was posted earlier. So Greybeard is most likely to have seen the links I have provided. I think Greybeard's answer is original with original research. I was only expecting a mention of the "not original answer by @tum_" and a link to his answer. Reasons as to why that answer was not adequate would have been a plus.
    – banuyayi
    Nov 10 at 15:33
  • 1
    It may be worth also adding emphasis to the comment in the etymology of hemi- that words formed from Greek tend to use hemi- and words from Latin tend to have semi- (with a note that the emphasis is not original), as this is an important distinction beyond the slight semantic differences (even if, as the quote notes, there is plenty of hybridism as well)
    – Tristan
    Nov 11 at 9:29

The simple answer would be what gained traction. Some people started using a particular compound word and that word then became widely used and it remained so.

Hemi- is Greek; Semi- is Latin; Demi- is French. They all mean some kind of "half."

This website: mentalfloss.com describes the minute differences in their meanings (hemi,semi,demi).

This answer by @tum_ details the origin of the prefixes in a related question previously asked on SE.


Semi- is Latin, hemi- is Greek, and demi- is French (and ultimately Latin, but from a different root than semi-).

When it doubt, use semi-. It's the most common of the three.

Hemi- is used for geometric (hemisphere, hemispheroid, but not semicircle) and biological (hemichordate, hemimetabolism, hemiparasitic) terms.

Demi- is used for demigod(dess), and obscure military terms (demibastion, demigorge, demilance, demilune).

Multiple halving prefixes are used in British music terminology for 32nd (demisemiquaver) and 64th (hemidemisemiquaver or semidemisemiquaver) notes.


Worth noting that hemisphere has a greek etymology for both the prefix and the main part (ἡμισφαίριον), same for semicircle and latin (semicirculus), that's why you wouldn't mix the prefixes in those cases.


I go with standard American usage. When an American uses "semi" as a noun, [s]he means a semi truck. If you're woozy, you're semiconscious, not demiconscious or hemiconscious.

Another canonical usage is demigod. No such thing as a semigod or a hemigod.

To sum up, in my experience almost all usage of these three prefixes is idiomatic.

  • 1
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  • But you can have a semi-demi-mini god Nov 11 at 18:58

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