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Compound Words

Compound words are formed when two or more words act together. The compound may be written as a single word (with no space between the joined words), with a hyphen between the joined words, or with spaces between the joined words:

  • footnote
  • ourselves
  • right-of-way
  • 3-minute break
  • delayed-reaction switch
  • land bank loan
  • parcel post delivery

The form of the compound varies with custom and usage as well as with the length of time the compound has existed.

Compound words usually begin as two or more separate, often unrelated words. When writers and speakers begin using the words together as nouns, verbs, adjectives, or adverbs, the compound generally has a hyphen or a space between words, depending on custom and usage. As the new compound becomes more common, the hyphen and space might drop, and the compound might be written as one word:

  • on-site has become onsite
  • co-operate has become cooperate
  • rail road has become railroad
  • auto body has become autobody

However, because of custom or usage, some compounds retain the hyphen or space between words:

  • all-inclusive
  • deep-rooted
  • living room
  • middle-sized
  • re-cover (to cover again)
  • re-create (to create again)
  • rough-coat (used as a verb)
  • sand-cast (used as a verb)
  • satin-lined
  • steam-driven
  • sugar water
  • summer school
  • terra firma
  • throw line
  • under secretary

Because new compound words are continually appearing in the language and because even familiar compounds might appear in different forms, depending on how they are used in a sentence, writers might have difficulty deciding which form of a compound to use. Recent dictionaries can often help by indicating how a word or compound has appeared previously.

However, for new compounds and for compounds not covered in dictionaries, use the principles of clarity and consistency, as well as the following guidelines, to select the form of the compound.

  1. Write compounds as two words when the compounds appear with the words in their customary order and when the meaning is clear:


    NOTE 1: Many such combinations are so common that we rarely think of them as compounds (especially because they do not have hyphens and are written with spaces between words). In many cases, writing them as a single word would be ridiculous: floodcontrol, realestate.

    NOTE 2: We continue to pronounce such compounds with fairly equal stress on the joined words, especially when one or more of the words has two or more syllables (as in social security).

  2. Write compounds as single words (no spaces between joined words) when the first word of the compound receives the major stress in pronunciation:

    • airplane
    • cupboard
    • doorstop
    • dragonfly
    • footnote
    • nightclerk
    • seaward
    • warehouse

    NOTE 1: The stress often shifts to the first word when that word has only one syllable, as in the preceding examples.

    NOTE 2: Words beginning with the following prefixes are not true compounds. Such words are usually written without a space or a hyphen:

    • afterbirth
    • Anglomania
    • antedate
    • biweekly
    • bylaw
    • circumnavigation
    • cooperate
    • contraposition
    • countercase
    • deenergize
    • demitasse
    • excommunicate
    • extracurricular
    • foretell
    • hypersensitive
    • hypoacid
    • inbound
    • infrared
    • interview
    • intraspinal
    • introvert
    • isometric
    • macroanalysis
    • mesothorax
    • metagenesis
    • microphone
    • misspelling
    • monogram
    • multicolor
    • neophyte
    • nonneutral
    • offset
    • outback
    • overactive
    • overflow
    • pancosmic
    • paracentric
    • particoated
    • peripatetic
    • planoconvex
    • polynodal
    • postscript
    • preexist
    • proconsul
    • pseudoscientific
    • reenact
    • retrospect
    • semiofficial
    • stepfather
    • subsecretary
    • supermarket
    • thermocouple
    • transonic
    • transship
    • tricolor
    • ultraviolet
    • unnecessary
    • underflow

    NOTE 3: Words ending with the following suffixes are not true compounds. Such words are usually written without a space or hyphen:

    • portable
    • coverage
    • operate
    • plebiscite
    • twentyfold
    • spoonful
    • kilogram
    • geography
    • manhood
    • selfish
    • meatless
    • outlet
    • wavelike
    • procurement
    • partnership
    • lonesome
    • homestead
    • northward
    • clockwise
  3. Hyphenate compounds that modify or describe other words:

    • rear-engine bracket
    • tool-and-die shop
    • two-phase engine-replacement program
    • down-to-cost model
    • two- or three-cycle process
    • 4-year plan
    • 20-day turn around
    • 2- or 3-week vacation


    NOTE 1: Such compounds are hyphenated only when they come before the word they modify. If the words forming the compound appear after the word they are describing, leave out the hyphens:

    • bracket for the rear engine (but rear-engine bracket)
    • a shop making tools and dies (but tool-and-die shop)
    • a program with two phases (but two-phase program)

    NOTE 2: When the meaning is clear, such compound modifiers may not need hyphens:

    • sick leave policy
    • land management plan
    • life insurance company
    • per capita cost
    • production credit clause
    • speech improvement class

    NOTE 3: Do not hyphenate if the first word of the compound modifier is an adverb ending with –ly:

    • barely known problem
    • eminently qualified researcher
    • highly developed tests
    • gently sloping range
    • however
    • well-developed tests
    • well-known problem
    • well-qualified researcher
  4. Treat compounds used as verbs as separate words:

    • to break down
    • to check out
    • to follow up
    • to get together
    • to go ahead
    • to know how
    • to run through
    • to shut down
    • to shut off
    • to stand by
    • to start up
    • to take off
    • to trade in

    The parallel compound nouns are usually either written as one word or hyphenated:

    • breakdown
    • checkout
    • follow-up
    • get-together
    • go-ahead
    • know-how
    • run-through
    • shutdown
    • shutoff
    • standby
    • start-up
    • takeoff
    • trade-in

    However, some verb phrases are identical to the compound noun form:

    • cross-reference (both a noun and a verb)

    When in doubt, check your dictionary.

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