Prefixes

Prefixes are letters which we add to the beginning of a word to make a new word with a different meaning. Prefixes can, for example, create a new word opposite in meaning to the word the prefix is attached to. They can also make a word negative or express relations of time, place or manner.

Here are some examples:

base word	prefixed word	type of meaning
possible	impossible	opposite
able	unable	opposite/negation
payment	non-payment	negation
war	pre-war	time (before)
terrestrial	extraterrestrial	place (outside of/beyond)
cook	overcook	manner (too much)

• I’m sorry I was unable to attend the meeting.
• Non-payment of fees could result in a student being asked to leave the course.
• Has anyone ever really met an extraterrestrial being? (meaning a being from another planet)
• The meat was overcooked and quite tasteless.

The most common prefixes

prefix	meaning	examples
anti-	against/opposed to	anti-government, anti-racist, anti-war
auto-	self	autobiography, automobile
de-	reverse or change	de-classify, decontaminate, demotivate
dis-	reverse or remove	disagree, displeasure, disqualify
down-	reduce or lower	downgrade, downhearted
extra-	beyond	extraordinary, extraterrestrial
hyper-	extreme	hyperactive, hypertension
il-, im-, in-, ir-	not	illegal, impossible, insecure, irregular
inter-	between	interactive, international
mega-	very big, important	megabyte, mega-deal, megaton
mid-	middle	midday, midnight, mid-October
mis-	incorrectly, badly	misaligned, mislead, misspelt
non-	not	non-payment, non-smoking
over-	too much	overcook, overcharge, overrate
out-	go beyond	outdo, out-perform, outrun
post-	after	post-election, post-war
pre-	before	prehistoric, pre-war
pro-	in favour of	pro-communist, pro-democracy
re-	again	reconsider, redo, rewrite
semi-	half	semicircle, semi-retired
sub-	under, below	submarine, sub-Saharan
super-	above, beyond	super-hero, supermodel
tele-	at a distance	television, telepathic
trans-	across	transatlantic, transfer
ultra-	extremely	ultra-compact, ultrasound
un-	remove, reverse, not	undo, unpack, unhappy
under-	less than, beneath	undercook, underestimate
up-	make or move higher	upgrade, uphill

Writing prefixes: hyphens (super-hero or supermodel)

There are no absolute rules for when to use a hyphen or when to write a prefixed word as one whole word (see the examples in the table). A good learner’s dictionary will tell you how to write a prefixed word.