35 Hyphens

A wise writer once said, “If you take hyphens seriously you will surely go mad.” Hyphens belong to that category of punctuation marks that will hurt your brain if you think about them too hard, and, like commas, people disagree about their use in certain situations. Nevertheless, if you learn to use hyphens properly, they help you to write efficiently and concretely, and you will have to use them regularly because of the nature of technical writing. Because concepts in science and engineering frequently rely on word blends and complex word relationships, the best writers in these fields master the use of the hyphen.

The Hyphen’s Function

Fundamentally, the hyphen is a joiner. It joins:

  • two nouns to make one complete word (kilogram-meter);
  • an adjective and a noun to make a compound word (accident-prone);
  • two words that, when linked, describe a noun (agreed-upon sum, two-dimensional object);
  • a prefix with a noun (un-American);
  • double numbers (twenty-four);
  • numbers and units describing a noun (1000-foot face; a 10-meter difference)
  • “self” and “well” words (self-employed, well-known);
  • ethnic labels (Irish-American);
  • new word blends (cancer-causing, cost-effective);
  • prefixes and suffixes to words, in particular when the writer wants to avoid doubling a vowel or tripling a consonant (anti-inflammatory; shell-like).

The rule of thumb I apply when using the hyphen is that the resulting word must act as one unit; therefore, the hyphen creates a new word—either a noun or a modifier—that has a single meaning. Usually, you can tell whether a hyphen is necessary by applying common sense and mentally excluding one of the words in question, testing how the words would work together without the hyphen. For example, the phrases “high-pressure system,” “water-repellent surface,” and “fuel-efficient car” would not make sense without hyphens, because you would not refer to a “high system,” a “water surface,” or a “fuel car.” As your ears and eyes become attuned to proper hyphenation practices, you will recognize that both meaning and convention dictate where hyphens fit best.


The following websites offer exercises on using the hyphen properly, as well as the correct answers to the exercise questions:

Hyphenation exercises from the Little, Brown Handbook

Hyphen practice from the Chicago-Kent College of Law

Examples of Properly Used Hyphens

Some examples of properly used hyphens follow. Note how the hyphenated word acts as a single unit carrying a meaning that the words being joined would not have individually.

small-scale study
two-prong plug
strength-to-weight ratio
high-velocity flow
well-known example
frost-free lawn
self-employed worker
one-third majority
coarse-grained wood
decision-making process
blue-green algae
air-ice interface
silver-stained cells
protein-calorie malnutrition
membrane-bound vesicles
phase-contrast microscope
long-term-payment loan
cost-effective program
time-dependant variable
radiation-sensitive sample
long-chain fatty acid

When Hyphens Are Not Needed

By convention, hyphens are not used in words ending in -ly, nor when the words are so commonly used in combination that no ambiguity results. In these examples, no hyphens are needed:

finely tuned engine blood pressure sea level
real estate census taker atomic energy
civil rights law public utility plant carbon dioxide

Prefixes and Suffixes

Most prefixes do not need to be hyphenated; they are simply added in front of a noun, with no spaces and no joining punctuation necessary. The following is a list of common prefixes that do not require hyphenation when added to a noun:

after anti bi bio co
cyber di down hetero homo
infra inter macro micro mini
nano photo poly stereo thermo

Common suffixes also do not require hyphenation, assuming no ambiguities of spelling or pronunciation arise. Typically, you do not need to hyphenate words ending in the following suffixes:

able less fold like wise

Commonly Used Word Blends

Also, especially in technical fields, some words commonly used in succession become joined into one. The resulting word’s meaning is readily understood by technical readers, and no hyphen is necessary. Here are some examples of such word blends, typically written as single words:

blackbody groundwater airship
downdraft longwall upload
setup runoff blowout


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Technical Writing by Lumen Learning is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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