I was introduced to the word “cul-de-sac” via an elementary school birthday party invitation. I found out that people didn’t just live on roads, streets, avenues, and lanes — they could also live on something named for a fancy French word, a cul-de-sac. “Cul” is an interesting word in French — it’s a rude slang word for someone’s rear end, but it’s used in some other contexts to refer to the end of something. The second half, “de sac,” means “of the bag” — so the literal translation of “cul-de-sac” is “bottom of the bag.” As a compound word, however, “cul-de-sac” means “dead end.” American housing developers borrowed it from French to name streets that are basically dead ends, where a few houses line the end of a road that goes nowhere. In planned subdivisions, they’re popular for privacy, parking, and a neighborhood camaraderie feel.
But say you live in a neighborhood that has many of these dead-end streets and your neighborhood association is trying to decide which one should host the summer block party. The correct pluralization of this compound word is “culs-de-sac,” not “cul-de-sacs.” While it may seem puzzling, it follows a grammar rule that affects many English words: In compound words, the chief element is pluralized, not the entire phrase.
Sure, the English language has plenty of irregular plurals, but in most cases, a suffix of “-s” or “-es” will suffice. But compound nouns — those formed by combining two or more words into one concept — aren’t as cooperative. You have to worry not only about what suffix to use, but also about where to use it. For instance, the “-s” suffix to pluralize “cul-de-sac” comes after the main noun “cul,” as in “culs-de-sac.”
This applies to other compound nouns, too. For instance, “mother-in-law,” “son-in-law,” and all other “in-law” honorifics are pluralized with an “-s” after the main noun, not the whole word. So, the correct terms are “mothers-in-law” or “sons-in-law.” Compound nouns made up of a main noun and a modifier, such as “passer-by,” “runner-up,” and “court-martial” get the same treatment — the correct plurals are “passers-by,” “runners-up,” and “courts-martial.” However, two-headed compound words, composed of two equal nouns (no modifier), tend to hyphenate only the final noun, as in “city-states” and “singer-songwriters.”
But it’s not only hyphenated compound words that face muddled pluralizations. Open compound words (featuring a space between words) also pose problems. “Surgeons general” and “chiefs of staff” are the correct plural forms because the main noun is pluralized, not the modifier. That said, you can likely get away with some pluralization missteps in casual conversation — a friend likely wouldn’t reprimand you for saying “sister-in-laws” or “cul-de-sacs.”
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