prefix

Everyday

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 →
2. To prefix something is to add a word, letters or numbers in front of it. tree →
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 →
4. A phone prefix (dialling code) is the numbers you dial before a phone number. tree →
5. To prefix a book or story can also mean to put an introduction or note at its very start. tree →

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 →
• The prefix re- means «again», as in «rewrite». tree →
• «Impossible» uses the prefix im-. tree →
• Kilo- is a prefix meaning a thousand, so a kilogram is 1,000 grams. tree →
• The prefix sub- means under, like in «submarine». tree →
• Circle the prefix in «disappear». tree →
• Milli- means one thousandth, so there are 1,000 millimetres in a metre. tree →
• To call another country, you prefix the number with its code. tree →
• 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 →

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 Jewish tradition

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.

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.