Hyphens are used to link words and parts of words.

Three main uses of the hyphen

  1. in compound words
  2. to join prefixes to other words
  3. to show word breaks 

1. Hyphens in compound words

Hyphens are used in many compound words to show a combined meaning

EXAMPLE:  a pick-me-up, mother-in-law, good-hearted 

Hyphens also show  that there is a relationship between the words that make up the compound:

EXAMPLE: rock-forming minerals are minerals that form rocks.

But you do not need to use them in every type of compound word.

Compound adjectives

Compound adjectives are made up of a noun + an adjective, a noun + a participle, or an adjective + a participle.

Many compound adjectives should be hyphenated. 

EXAMPLES:

noun + adjective

noun + participle

adjective + participle

accident-prone

computer-aided

good-looking

sugar-free

power-driven

quick-thinking

carbon-neutral

user-generated

bad-tempered

sport-mad

custom-built

fair-haired

camera-ready

muddle-headed

open-mouthed


Use a hyphen with compound adjectives formed from the adverb well and a participle  

EXAMPLE: well-known

Use a hyphen with compound adjectives formed from a phrase 

EXAMPLE: up-to-date

Use a hyphen with compound adjectives formed when the compound comes before the noun:

EXAMPLE: well-known brands of coffee

But do not use the hyphen when the compound comes after the noun:

EXAMPLE: His music was also well known in England.

EXAMPLE: Their figures are up to date.

It’s important to use hyphens in compound adjectives describing ages and lengths of time: leaving them out can make the meaning ambiguous.

EXAMPLE: 250-year-old trees (clearly refers to trees that are 250 years old, while 250 year old trees might also refer          to 250 trees that are all one year old.)

Compound verbs

Use a hyphen when a compound formed from two nouns is made into a verb, for example:

 EXAMPLES:

noun

verb

an ice skate

to ice-skate

a booby trap

to booby-trap

a spot check

to spot-check

Phrasal verbs

You should NOT put a hyphen within phrasal verbs ie.verbs made up of a main verb and an adverb or preposition. 

EXAMPLES:

Phrasal verb

Example

build up

You should continue to build up your pension.

break in

They broke in by forcing a lock on the door.

stop off

We stopped off in Hawaii on the way home.

If a phrasal verb is made into a noun, though, you SHOULD use a hyphen:

 EXAMPLES:

Noun

Example

build-up

There was a build-up of traffic on the ring road.

break-in

The house was unoccupied at the time of the break-in.

stop-off

We knew there would be a stop-off in Singapore for refuelling.

Compound nouns

A compound noun is one consisting of two component nouns. In principle, such nouns can be written in one of three different ways.  So prepare to see all of these different ways of writing compound nouns in your reading of various English texts.

 EXAMPLES:

one word

two words

hyphenated

bootcamp

boot camp

boot-camp

spellchecker

spell checker

spell-checker

chatroom

chat room

chat-room

use two words to form a compound noun

We, at the UT, recommend you use two words to form compound nouns. 
EXAMPLE: boot camp

However, the most important thing to note is that you should choose one style and stick to it within a piece of writing.

AVOID:  bootcamp in one paragraph and then boot camp in another


2. Hyphens joining prefixes to other words

Hyphens can be used to join a prefix to another word, especially if the prefix ends in a vowel and the other word also begins with one

EXAMPLE: pre-eminent or co-own

Use a hyphen to separate a prefix from a name or date

EXAMPLE: post-Aristotelian or pre-1900

Use a hyphen to avoid confusion with another word:

EXAMPLE: to distinguish re-cover (= provide something with a new cover) from recover (= get well again).


3. Hyphens showing word breaks

Hyphens can also be used to divide words that are not usually hyphenated. They show where a word is to be divided at the end of a line of writing. Always try to split the word in a sensible place, so that the first part does not mislead the reader:

EXAMPLE: hel-met 

AVOID: he-lmet

Hyphens are also used to stand for a common second element in all but the last word of a list:

EXAMPLE: You may see a yield that is two-, three-, or fourfold.


The em dash, or long dash (–)

An em dash, or long dash, is used for two reasons:

 1. to mark off information or ideas that are not essential to an understanding of the rest of the sentence (use a pair of dashes):

EXAMPLE: Thousands of children—like the girl in this photograph—have been left homeless.

2. to show other kinds of break in a sentence where a comma, semicolon, or colon would be traditionally used:

EXAMPLE: One thing’s for sure—he doesn’t want to face the truth.

EXAMPLE: Things have changed a lot in the last year—mainly for the better.

Note that there is no space added on either side of an em dash.

Em dashes are especially common in informal writing, such as personal emails or blogs, but it’s best to use them sparingly when you are writing formally.

The en dash, or short dash (–)

The en dash is slightly longer than the hyphen but not as long as the em dash. (It is, in fact, the width of a typesetter’s letter “N,” whereas the em dash is the width of the letter “M”—thus their names.) The en dash means, quite simply, 'through.'

We use it most commonly to indicate inclusive dates and numbers

EXAMPLE: July 9–August 17; pp. 37–59.

Note that there is no space added on either side of an en dash.

Typing the em dash 

The ee dash can be typed as Alt + 0151

Typing the en dash

The en dash can be typed as Alt + 0150


References and further tips 

Oxford Dictionaries Blog. 'How to use hyphens'. Retrieved from https://blog.oxforddictionaries.com/2011/10/11/hyphens-in-the-headlines/

Get it Write. 'En Dashes and Em Dashes'. Retrieved from https://getitwriteonline.com/articles/en-dashes-em-dashes/ 

Oxford Living. 'punctuation/hyphen' Retrieved from https://en.oxforddictionaries.com/punctuation/hyphen