Student Stumper 11: Compound Words

QUESTION: How do we know if a compound word is written as a single word, as separate words, or with a hyphen?

ANSWER: Look it up in the dictionary.

I love a question that allows me to give a clear and satisfying answer to a student. Unfortunately, not all questions are like this. The question above about compound words is one that doesn’t lead to immense gratitude from the questioner when I tell the answer. There isn’t one simple rule that makes it easy to know if a compound word is closed (one word), open (two or more words), or hyphenated. This question can cause as much frustration for language learners as questions about gerunds v. infinitives or separable v. inseparable phrasal verbs.

However, compound rules do follow some patterns. Awareness of them will lead to greater accuracy when writing compound words. Most sources I’ve checked agree on the following:

  • Compound modifiers with numbers: Hyphenate these modifiers before nouns. Example: a thirty-year-old man. Note the use of the singular unit year. Contrast it with the plural form in this word order: The man is thirty years old.
  • Compound modifiers with past participles: These modifiers are hyphenated. Examples: age-related, web-based, drug-induced.
  • Color combinations: These modifiers are hyphenated. Example: a blue-green scarf.
  • Well-known compounds: Some compounds involving three or more words are so common that there’s little if any chance of confusion, so open forms are used. Examples: a ham and cheese sandwich, high school students, parking lot attendant.

I’d like to add these patterns and see if others agree or wish to challenge them:

  • Compound words with numbers: If the numbers are not being joined with common nouns used for weights and measures (such as year, pound, page), a hyphenated form is used as a modifier, an adverb, and a complement. Example: A two-handed throw. / He threw the ball two-handed. / The throw was two-handed. Similar compounds: two-headed, one-armed, three-legged, one-eyed.
  • Compound modifiers with present participles: They are hyphenated just as the [noun + past participle] combination is. Examples: ever-changing, all-knowing, fast-growing.
  • Compounds with of and only: These multi-word compounds are hyphenated. Examples: state-of-the-art, man-of-war, read-only, text-only.
  • Compound words with in-law: These compound nouns are hyphenated. Examples: mother-in-law, brother-in-law, daughter-in-law. 
  • Compound words with great: These compound nouns are hyphenated. Examples: great-aunt, great-grandfather, great-grandchildren.
  • Compounds with single letters: These compounds are hyphenated. Examples:  a U-turn, an A-frame, L-shaped, x-ray, t-shirt.
  • Directional compounds: These are closed forms. Examples: northeast, northeastern. Exception: if a range is implied a hyphen is used between the two possible directions. Example: travel south-southwest.

Do you need to present the concept of compound words to your students? These short clips may be of help. They’re based on the work done by elementary school children:

Do you need ideas to help students practice using compound words? Check back soon. I’ll offer an activity in my next posting.


Mauer, Jay. Focus on Grammar: An advanced course for reference and practice. Longman: 2000.

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