Compound Adjectives

Let’s take a look at the following sentence:

Bad Example (but good news):
Oil production has increased during this six-months period.

As with all critiques, we will start off by saying something positive: the hyphen definitely belongs there. However, the “S” at the end of “months” does not.

“Why?” you may ask. “There are six months, and that is more than one, so it should be plural, right?”

No. The reason is that the compound adjective, six-month, is an adjective, and in the English language adjectives do not have plurals.
Only when “month” is standing alone and functioning as a noun does it become plural.

Corrected Examples:
Oil production has increased during this six-month period. (compound adjective)
Oil production has increased during these six months. (noun)

Other good examples of singular compound adjectives:
Two-bit geologist
Three-penny opera
Four-bedroom house
Five-dollar bill
Six-inch nails
Seven-layer cake
Eight-piece jazz band
Nine-digit account number
Ten-mile hike

Post-Election Day Quote:
“Ballots are the rightful and peaceful successors to bullets.”
– Abraham Lincoln, 16th President of the United States, 1809–1865


2 Responses to “Compound Adjectives”

  1. petrocomputing Says:

    Don in Houston asks:
    How about…
    2-bit geologist
    3-penny opera
    4-bedroom house
    5-dollar bill
    6-inch nails
    7-layer cake
    8-piece jazz band
    9-digit account number
    10-mile hike

    • petrocomputing Says:

      Dear Don:
      These would be hyphenated and also singular.
      However, the SPE Style Guide would have you spell out the numbers from one to nine unless there is a unit of measure (inch, mile) immediately after it.
      And we would probably say $5 bill in a technical paper, but spell out five-dollar bill in a thank-you note.
      – Jeanne

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