Compound modifier

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Compound modifiers are two or more words that together describe a noun, like man-eating or one-way. They can come before a noun (attributive) or after a linking verb (predicative).

- Hyphenation before a noun: when the compound modifier precedes the noun, it’s usually hyphenated (heavy-metal detector) to keep the meaning clear. Without the hyphen, heavy metal detector can mean a detector that is heavy.
- After the noun: when the modifier comes after the noun, it’s typically not hyphenated (the detector is heavy metal).
- Open vs. hyphenated: open compounds (heavy metal detector) exist, but hyphenated forms are clearer.
- Dictionary guidance: some compounds are fixed words listed in dictionaries. Follow the dictionary’s hyphenation.
- Numerals: if a numeral + noun acts as a modifier before the noun, hyphenate (12-furlong race, eight-horse race).
- When both parts are nouns: usually no hyphen is needed.
- Adverbs: quickly and badly are usually not hyphenated; well-known uses a hyphen (well-known actress) when before the noun, but well known after the noun is separate (the actress is well known).
- Readability: hyphens help avoid misreading; an en dash can also be used for clarity.
- Other languages: rules differ. For example, in Japanese some na-adjectives form compounds; i-adjectives do so less often.

In short: use hyphens to link words that work together to describe a noun, especially before the noun, to prevent confusion.