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# prefix

«prefix» in Mova's school dictionary: **a group of letters added to the start of a word to make a…** — its meaning for a pupil, its sense in the lessons and examples, with 5 sentences of Mova's corpora that use it.

### part of speech

noun (a prefix, prefixes); verb (prefix, prefixes, prefixed, prefixing)

### meaning for a pupil

1) A prefix is a group of letters added to the start of a word to make a new word with a different meaning, like un- in «unhappy», re- in «redo» or pre- in «preview». [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#m1)

2) To prefix something is to add a word, letters or numbers in front of it. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#m2)

3) In maths and science, prefixes on units show size: kilo- means a thousand (kilometre), centi- means a hundredth (centimetre), milli- means a thousandth (millimetre). [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#m3)

4) A phone prefix (dialling code) is the numbers you dial before a phone number. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#m4)

5) To prefix a book or story can also mean to put an introduction or note at its very start. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#m5)

### sense in the lessons

In English grammar and spelling lessons (and SATs), prefixes change meaning but not spelling of the root: un- and dis- and in-/im-/il-/ir- make opposites (unkind, disagree, impossible, illegal, irregular); re- means again; pre- means before; sub- means under; super- means above; anti- means against; auto- means self. In maths lessons, unit prefixes help convert measures. Phrases: add a prefix, the prefix un-, negative prefix.

### examples

- Add the prefix un- to «tidy» to make «untidy». [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x1)
- The prefix re- means «again», as in «rewrite». [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x2)
- «Impossible» uses the prefix im-. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x3)
- Kilo- is a prefix meaning a thousand, so a kilogram is 1,000 grams. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x4)
- The prefix sub- means under, like in «submarine». [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x5)
- Circle the prefix in «disappear». [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x6)
- Milli- means one thousandth, so there are 1,000 millimetres in a metre. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x7)
- To call another country, you prefix the number with its code. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x8)
- This introduction is almost identical with that prefixed to the German story of "Allerleirauh,"[195] except in so far as the puppets are concerned. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/#x9)

### note

Countable: a prefix, prefixes (add -es after x). Pronounced «PREE-fix». A prefix goes at the START; a suffix goes at the END. Spelling trap: adding a prefix does not change the root's letters, so double letters can appear: dis + satisfied = dissatisfied, mis + spell = misspell, un + necessary = unnecessary. In maths: kilo- = ×1,000; centi- = ÷100; milli- = ÷1,000.

### In the corpora

- [The best news for spellers: a prefix never changes the spelling of the root word.](https://md.mova.elamur.ai/free/en/corpora/school/english/12-prefixes-un-dis-mis-re-pre-in-im-il-ir/1/)
- [Write the prefix, then the whole word, letter for letter.](https://md.mova.elamur.ai/free/en/corpora/school/english/12-prefixes-un-dis-mis-re-pre-in-im-il-ir/2/)
- [The doubles are not mistakes; they are the end of the prefix meeting the start of the word.](https://md.mova.elamur.ai/free/en/corpora/school/english/12-prefixes-un-dis-mis-re-pre-in-im-il-ir/4/)
- [Prefixes let you guess new words.](https://md.mova.elamur.ai/free/en/corpora/school/english/12-prefixes-un-dis-mis-re-pre-in-im-il-ir/9/)
- [A prefix is added to the start of a word and changes its meaning.](https://md.mova.elamur.ai/free/en/corpora/school/english/12-prefixes-un-dis-mis-re-pre-in-im-il-ir/12/)

### Trees and pragmatics

[Every meaning and example of «prefix» parsed by Mova](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/P/prefix/), each sentence with its dependency tree and frames.