We use prefixes to change meaning. Unlike suffixes, prefixes rarely change the part of speech. Many prefixes give a word a meaning which is the opposite or negative of the original. For example:

dis + satisfaction = dissatisfaction

un + clear = unclear

COMMON PREFIXES, THEIR MEANINGS & EXAMPLES

• anti + adjective/noun → opposite, against → anti-Semitic, anti-clockwise, anti-European
• counter + adjective/noun → against → countermeasure, counterproductive, counterattack
• de + verb/noun → opposite, remove, reduce → decompose, decentralize, decontaminate
• dis + verb → opposite, negative → dislike, dissatisfy, dismantle
• il + adjective → opposite → illegal, illogical, illegible
• im + adjective → opposite → impossible, immortal, impolite
• in + adjective → opposite → indirect, incomplete, insecure
• ir + adjective → opposite → irresponsible, irritated, irrational
• pro + adjective/noun → in favor of → pro-European, proactive, pro-democracy
• co + noun/verb → together → cooperation, cooperate, coordinate
• tele + noun→ at a distance → telegraph, telephone, television
• inter + adjective → between → intercontinental, international, interracial
• trans + adjective/noun/verb → across → transcontinental, transatlantic, transmission
• mis + verb → wrongly/badly → misunderstand, mistake, misinterpret
• under + verb → not enough, too little → underestimate, underuse, underfund
• out + verb → more → outrun, outnumber, outperform
• post + noun/verb → after → postgraduate, postmortem, post-election
• pre + noun/verb → before → preparation, prearrange, pre-war
• ex + noun → previous → ex-girlfriend, ex-president, ex-colleague
• extra + adjective → beyond, outside of → extraterrestrial, extracurricular, extraordinary
• down + noun → lower, reduce → downsize, downtown, downhill
• up + noun → upwards, upper → uptown, upmarket, uphill
• over + verb → too much → overdo, overreact, overestimate
• sub + adjective/noun → below → substandard, subcommittee, submarine
• semi + noun/adjective → half, partly → semidarkness, semiskilled, semicircle
• super + noun/adjective → greater than → supernatural, superhuman, superman
• ultra + noun/adjective → on the far side of, beyond → ultrasound, ultramodern, ultra-ambitious
• hyper + noun/adjective →  too much → hypertension, hyper-fit, hypercritical
• hypo + noun/adjective → under, lower, less than → hypotension, hypothermia, hypotensive
• un + verb/adjective → opposite, negative → un-do, un-break, uneven
• mega + noun/adjective → great, important → megastar, mega-deal, megabyte
• macro + noun → large → macroeconomics, macro-relationship (technical term) 
• mini + noun → small → miniskirt, minivan, miniseries
• micro + noun → very small → microorganism, microsecond, microscope
• mono + noun/adjectives → one → monolingual, monopoly, monologue
• multi + noun/adjective → many → multipurpose, multilingual, multinational
• non + noun/adjective → negative → non-payment, non-stop, non-citizen
• auto + noun→ autopilot, autobiography, automobile
• mid + noun → middle → midday, midnight, midwest
• re + verb → again → reform, reconsider, reconstruct

Note that we use il- instead of in- with words that begin with l: illogical, illegal, illegible. We use im- instead of in- with words that begin with m or p: impolite, improper, immortal.  We often use ir- instead of in– with words that begin with r: irresponsible, irresistible, irrational.

It’s also important to note that many words with a prefix have a base part that never exists on its own. For example, postmortem, immediate, incontrovertible.

It’s often difficult to guess which prefix should be used with a word to change its meaning. Please use a dictionary when you are not sure which prefix to use.

WORD BUILDING PRACTICE

For questions 1-12, read the text below. Use the word given in capitals to form a word that fits the space.

The Government has decided to take the (1) ________ (POPULAR) decision to ban smoking in a lot of public places. Through many people find smoking (2) ________ (PLEASE), and though experts all agree it is (3) ________ (HEALTH) and that it costs the state a lot to treat victims of smoking, it is also (4) ________ (DENY) that many people get pleasure from the habit and find smoking (5) ________ (RESIST) when they are in company. However, it is now (6) ________ (POSSIBLE) to deny the (7) ________ (SOCIAL) nature of the habit. As advertising has proved (8) ________ (EFFECT) with many smokers, the Government has now made smoking (9) ________ (LEGAL) in most public places.

Smokers who are (10) ________ (ABILITY) to stop smoking will be obliged to enjoy their pastime in private and may feel the new measures are (11) ________ (JUSTICE), but for passive smokers for whom a room full of smokers is (12) ________ (BEAR) they will come as a breath of fresh air.

Answer key: 1. unpopular 2. unpleasant/displeasing 3. unhealthy 4. undeniable 5. irresistible 6. impossible 7. antisocial 8. ineffective 9. illegal 10. unable 11. unjust 12. unbearable

Materials used: “Grammar and Vocabulary for First Certificate” by L.Prodromou

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