Prefixes are one of the fastest ways to grow your English vocabulary. Once you know that re- means “again,” pre- means “before,” and un- often means “not,” many unfamiliar words become much easier to understand.
A prefix is a group of letters added to the beginning of a word to change its meaning. For example, happy becomes unhappy, and write becomes rewrite.
List of Prefixes
Continue building your word-formation skills with related lesson:
- Suffixes in English – Learn how endings such as -ful, -less, -able, and -tion change a word’s meaning and part of speech.
Negative Prefixes
These prefixes often create the opposite meaning of a word or show that something is not true, not allowed, or not complete.
| Prefix | Meaning | Example Words | Example in Context |
|---|---|---|---|
| un- | not; opposite of | unhappy, unsafe, unfair | She felt unhappy after hearing the bad news. |
| dis- | not; opposite; remove | disagree, dishonest, disappear | I strongly disagree with that decision. |
| non- | not; without | nonfiction, nonstop, nonverbal | This is an excellent nonfiction book about history. |
| in- | not | inactive, incomplete, invisible | The account stayed inactive for several months. |
| im- | not | impossible, impatient, imbalance | It is impossible to finish the report without the missing data. |
| il- | not | illegal, illogical, illegible | The signature was almost illegible on the old document. |
| ir- | not | irregular, irresponsible, irrelevant | His answer was irrelevant to the interview question. |
Time, Order, and Place Prefixes
These prefixes help describe when something happens, where something is located, or how it relates to another thing.
| Prefix | Meaning | Example Words | Example in Context |
|---|---|---|---|
| pre- | before | preview, pretest, prewar | We watched a short preview before the film was released. |
| post- | after | postgraduate, postnatal, postgame | She enrolled in a demanding postgraduate course. |
| fore- | before; in advance | forecast, foresight | The weather forecast helped us plan the outdoor event. |
| mid- | middle | midterm, midnight | Students started reviewing two weeks before the midterm. |
| sub- | under; below | submarine, subway | The submarine moved quietly beneath the surface. |
| inter- | between; among | international, intermission | She works for an international company with offices in five countries. |
| trans- | across; through | transport, transfer | The hospital plans to transfer the patient to a specialist clinic. |
Action and Degree Prefixes
These prefixes change the strength, direction, or repetition of an action.
| Prefix | Meaning | Example Words | Example in Context |
|---|---|---|---|
| re- | again; back | rewrite, rebuild, reconnect | Please rewrite this paragraph so the meaning is clearer. |
| mis- | wrong; badly | misjudge, misunderstand | I think you misunderstood the instructions. |
| over- | too much | overwork, overcook | Do not overcook the vegetables if you want them to stay crisp. |
| super- | above; beyond | superstar, superhuman | The athlete showed almost superhuman strength during the final round. |
| semi- | half; partly | semicircle, semifinal | The team reached the semifinal after winning three matches. |
| auto- | self | automatic, autopilot | The plane switched to autopilot during the long flight. |
| anti- | against | antivirus, antisocial | Install antivirus software before opening unknown files. |
| ex- | former | ex-president, ex-manager | He met his ex-manager at a business conference. |
Common Prefixes in Science, Math, and Medicine
These prefixes appear often in school subjects, medicine, technology, and academic vocabulary.
| Prefix | Meaning | Example Words | Example in Context |
|---|---|---|---|
| bio- | life | biome, biosphere | Climate change can affect every biome on Earth. |
| geo- | earth | geography, geology | She studies geology because she is fascinated by rocks and volcanoes. |
| astro- | space | astronomy, astronaut | The child became interested in astronomy after seeing Saturn through a telescope. |
| mono- | one | monomial, monologue | The actor delivered a powerful monologue at the end of the play. |
| poly- | many | polygon, polyglot | A polyglot can speak several languages fluently. |
| deca- | ten | decagon, decade | The city changed dramatically over the past decade. |
| kilo- | thousand | kilogram, kilometer | The nearest village is five kilometers away. |
| centi- | hundredth | centimeter, centipede | The fabric shrank by two centimeters after washing. |
| milli- | thousandth | millisecond, millimeter | In online gaming, even one millisecond can make a difference. |
| hypo- | below; under | hypoglycemia, hypothermia | Hypothermia can happen when body temperature drops too low. |
| hyper- | above; excessive | hyperactive, hypertension | The doctor monitored him for signs of hypertension. |
| epi- | on; upon | epidermis, epidemic | The epidermis is the outer layer of skin. |
Mini Quiz: Test Your Understanding
Choose the best answer.
- Choose the correct prefix: ___legal
a) in-
b) il-
c) im- - Choose the correct prefix: ___possible
a) im-
b) ir-
c) un- - What does pre- mean?
a) after
b) before
c) not - Choose the correct word:
a) disunderstand
b) misunderstand
c) ununderstand - Which prefix means “again”?
a) re-
b) anti-
c) post- - Which word means “too much work”?
a) rework
b) overwork
c) forework
Answer Key
- b) il- — il- is used before words beginning with l: illegal.
- a) im- — im- is used before p: impossible.
- b) before — pre- means before.
- b) misunderstand — mis- means wrong or badly.
- a) re- — re- means again.
- b) overwork — over- means too much.
Key Takeaways
🔤 Prefixes Change Meaning
Prefixes are added to the beginning of a base word to create a new meaning.
happy → unhappy
🚫 Negative Prefixes Follow Letter Patterns
Use il- before l (illegal), im- before p, m, b (impossible), and ir- before r (irregular).
🗺️ Time & Place Prefixes
These prefixes help describe time and position:
pre- = before
post- = after
inter- = between
sub- = under
Last Updated on July 9, 2026
