What is a prefix?
A prefix is a group of letters added to the beginning of a word. A prefix changes the word’s meaning.
- happy → unhappy (not happy)
- read → reread (read again)
- view → preview (view before)
The word the prefix is added to is called the base word. Sometimes a prefix is added to a root instead, a word part from Latin or Greek that cannot stand alone, like -ject in reject or -port in transport. Prefixes and suffixes together are called affixes.
Why prefixes are powerful
Learning one prefix helps you understand dozens of words. If you know that pre- means "before", you can work out preheat, preschool, prehistoric, preview and predict. Studies show that just four prefixes, un-, re-, in- and dis-, appear in more than half of all English words that have prefixes.
The most common prefixes
| Prefix | Meaning | Examples |
|---|---|---|
| un- | not, opposite | unkind, unlock, unfair |
| re- | again, back | redo, return, rebuild |
| dis- | not, opposite | dislike, disagree, disappear |
| in-, im-, il-, ir- | not | incorrect, impossible, illegal, irregular |
| pre- | before | preview, prepay, preschool |
| mis- | wrongly | misspell, mislead, misplace |
| non- | not | nonstop, nonfiction, nonsense |
| over- | too much | overeat, overflow, oversleep |
| under- | too little, below | underpaid, underground |
| sub- | under | submarine, subway, subtract |
| inter- | between | international, interrupt |
| trans- | across | transport, transatlantic |
| super- | above, beyond | superhero, superstar |
| anti- | against | antifreeze, antibiotic |
| co- | together | cooperate, coworker |
Number prefixes
| Prefix | Meaning | Examples |
|---|---|---|
| uni-, mono- | one | unicycle, monorail |
| bi- | two | bicycle, bilingual |
| tri- | three | triangle, tricycle |
| quad- | four | quadrilateral |
| pent- | five | pentagon |
| dec- | ten | decade |
| cent- | hundred | century, centimetre |
Negative prefixes: which one?
Several negative prefixes mean "not". The base word decides which one is used:
- im- usually comes before b, m or p: impossible, immature, imbalance
- il- before l: illegal, illogical
- ir- before r: irregular, irresponsible
- in- before most other letters: incomplete, invisible
Un- and dis- follow less predictable patterns, so use a dictionary when unsure.
Spelling with prefixes
Adding a prefix never changes the spelling of the base word. Just attach it.
- mis + spell = misspell (two s’s)
- un + necessary = unnecessary (two n’s)
- dis + satisfied = dissatisfied (two s’s)
- il + legal = illegal (two l’s)
When to use a hyphen
Most prefixes join directly. Use a hyphen when:
- The base word starts with a capital letter: pre-Confederation, un-Canadian
- The prefix is ex- (former) or self-: ex-champion, self-confidence
- Two of the same vowels would meet: re-enter, co-owner
- The meaning could be confused: re-cover (cover again) vs recover (get better)
Breaking long words apart
Prefixes help with long words. Cover the prefix, read the base word, then add the prefix back:
un | believ | able → unbelievable
dis | agree | ment → disagreement
Worked examples
Example 1: What does misbehave mean? → mis- (wrongly) + behave = to behave wrongly.
Example 2: Add the correct "not" prefix. ___possible, ___legal, ___visible → impossible, illegal, invisible.
Example 3: Add un- to natural. → unnatural (keep both n’s).
Common mistakes
- mispell ✗ → misspell ✓
- unecessary ✗ → unnecessary ✓
- inpossible ✗ → impossible ✓
- Thinking every word starting with these letters has a prefix: uncle and reach do not.
Try it yourself
- Add a prefix to make the opposite: agree, lock, polite, honest.
- What do bi- and tri- mean? Give an example of each.
- What does preheat mean?
- Spell correctly: un + noticed, dis + similar.
Answers: 1. disagree, unlock, impolite, dishonest. 2. Two (bicycle) and three (triangle). 3. To heat before. 4. unnoticed, dissimilar.
Tip for families
Play "Prefix builder" with cards. Put prefixes (un, re, pre, dis) on one colour of card and base words (do, play, like, view, happy) on another. Take turns building real words and explaining what they mean.
Quick recap
- A prefix goes at the beginning of a word and changes its meaning.
- un-, re-, in- and dis- are the most common.
- Adding a prefix does not change the base word’s spelling.
- Knowing prefixes helps you read and understand long words.