Lesson: Hyphenation of Compound Words

Compound words, such as health science, meta-analysis or reevaluation, are combinations of two or more terms that function to express a single idea. For native and non-native English speakers alike, knowing when to hyphenate a compound word can be troublesome. This is because compound nouns evolve over time in English (e.g. re-evaluation → reevalation; post-operative → postoperative; white light endoscopy → white-light endoscopy → whitelight endoscopy) and it is not always clear at what point in its evolution the word currently is. Also, unfortunately, English is not always consistent!

To find out whether or not to hyphenate compound words in common use, consult a dictionary (the latest version!). Examples of the dictionaries recommended by scientific bodies (e.g., the American Medical Association, American Chemical Society and American Psychological Association) as well as journals include Merriam-Webster’s Collegiate Dictionary, Webster’s New World College Dictionary and the Oxford English Dictionary .

To determine whether or not to hyphenate compound words not in common use but often found in scientific writing, a few general rules will help you to determine when to hyphenate.

Read on to learn some of these general rules, or jump straight to testing your knowledge on our short quizzes.

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Compound words should, in principle, be hyphenated in the situations listed below.

Please note, however, that in scientific and medical fields there is a trend to avoid hyphenation (e.g. “antiadhesive” cf. “anti-adhesive”, “abovementioned” cf. “above-mentioned”, although both the hyphenated and non-hyphenated terms are in common use). Check recent papers and the Guidelines for Authors in your target journal/publication to determine the preferred style.

Source documents are provided for all the examples given below so you can see how the example compound words are used in context in technical papers.

General rules

1. When an adjective and a noun are combined in a compound word and that compound word modifies the noun it precedes.

high-performance material	Source: G. Hart, Nature Materials 2007;6:941-945.
energy-efficient lamps	Source: Menanteau & Lefebvre, Research Policy 2001;29:375-390.

2. When a compound word is a fraction used as an adjective.

one-fifth increase	Source: Jackson et al., Oecologia 1998;113:537-546.
two-thirds majority	Source: Behrens et al., Cornea 2006;25:900-907.

3. When two verbs are combined in a compound word.

freeze-dry	Source: Meister & Gieseler, Journal of Pharmaceutical Sciences 2009;98:3072-3087.
jump-start	Source: Layden et al., Journal of Viral Hepatitis 2002;9:340-345.

4. When a verb that is used as an adjective is combined with another term in a compound word and that compound word modifies the noun it precedes.

anxiety-arousing conditions	Source: Sherwood & Potash, Journal of Clinical Psychology 1988;44:817-820.
decision-making methods	Source: P. Jankowski, International Journal of Geographical Information Science 1995;9:251-273.

5. When the first term in a compound word is a number and that compound word modifies the noun it precedes.

three-fold increase	Source: Campbell et al., PLoS One 2011;6:e18688.
2-hour pretreatment	Source: Herman et al., Pharmacology 1982;24:111-117.

6. When one of the terms in a compound word is a preposition.

trade-off	Source: Dupont et al., Journal of Experimental Biology 2010;213:1143-1152.
go-between	Source: Fey & Ramsay, World Politics 2010;62:529-560.