Special cases of compound words

Certain categories of compound words follow their own rules.

Compass directions

Set simple compass directions solid:

northeast     southwest     Southeast Asia

and complex directions with a hyphen:

east-northeast     south-southwest

When ‘from’ and ‘to’ are implied in the sentence, use an en dash:

The fire moved in an east–west direction.

Age terms

Use the following forms:

a 5-year-old child     a child aged 5 years     a group of 5-year-olds
a child who is 5 years old

Numbers expressed in words

Hyphenate numbers between 21 and 99 expressed in words:

forty-five     one hundred and forty-five

Fractions expressed in words

Hyphenate simple fractions expressed in words:

one-third     three-quarters   but   one twenty-fifth

Expressions of quantities with units

Do not use a hyphen when the unit is abbreviated, but use a hyphen when the unit is spelled out in full:

a 20 L container     a 20-litre container 

the 100 m race     the 100-metre race

Chemical names

Use a hyphen to set off numerals used as locants within a chemical name (see Locants, descriptors and isomers):

2-hydroxymethyl-1-methyl-5-nitroimadazole     2,4,5-T

Proper nouns relating to geography

Use a hyphen in compound adjectives relating to geography where the first term is a prefix:

Indo-Pacific region

but use an en dash where the components have equal weight:

Asia–Pacific region

Phrases with italics, capital letters, quotation marks or numbers

Do not hyphenate phrases set in italics, in quote marks, with capital letters or containing numbers:

an annus horribilis period     a ‘she’ll be right’ attitude     a High Court ruling     type 1 diabetes

Foreign phrases

Do not hyphenate foreign phrases that consist of more than 1 word:

an à la carte menu     in vitro fertilisation


Describing shades of colour with the available words for colour can be difficult. Writers on fashion, decor and architecture, as well as scientists (eg botanists, entomologists), may use established compound terms or invent ones to express the colours of the objects they are describing.

Follow these key principles for writing compound colour names.

Do not hyphenate compound colour names that have a long history of use:

crimson red     olive green     navy blue     lipstick pink

For colour combinations in which each colour has equal weight, use an en dash:

The curtains are printed with a yellow–brown pattern.

Grey–green larvae hatch from the insect’s eggs.

Blue–green algae produce toxins that can harm animals.

For compound adjectives that include colours with modifiers based on other colours (eg creamy, bluish, reddish), or on shade or intensity (eg pale, dull, dark, light, deep):

  • include a hyphen when used before the noun they modify

Creamy-white armchairs lighten the tone of the room.

A dark-brown carpet made the room appear gloomy.

The defining symptom of rust is the presence of tan-to-dark-brown or reddish-brown spots on the leaves.

We gazed for hours at the deep-blue sea.

  • do not hyphenate when used after the noun they modify

Leaves are bluish green.

Larvae are initially creamy white but develop black marks.

Download our quick guide for reference: Using words to describe colours .

When words just won’t do …

The guesswork can be taken out of colour descriptions by quoting the relevant PantoneR colour. The Pantone Colour Matching System (PMS) is a standardised colour reproduction system. Pantone colour guides are used worldwide for accurate colour identification and design specification.

Considering the complexity of describing colours in words, in some cases it might be more accurate to use Pantone colours when describing individual colour shades or ranges of colour.

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