Is there a rule to explain why (in most dictionaries) words such as half-brother or half-sister are hyphenated while stepbrother or stepsister are not?

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    For what it's worth, Merriam-Webster and American Heritage appear to render it "half sister", which is the spelling I've personally encountered the most. Unfortunately I don't know a good answer to the larger question other than "that's just how it is." Dec 19, 2016 at 15:00
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    As words evolve over time, you often see the phenomenon where noun phrases will become hyphenated words, and where hyphenated words become a single word. English is mutable that way, and you can't predict today what general usage will be 100 years from now. People used to spell "coordinate" as "co-ordinate" or "coördinate".
    – John Feltz
    Dec 19, 2016 at 16:05
  • @John Feltz: I do agree with you on language(s) changing over time and this could be seen in different ways of using some words (e.g. bookshop, book shop, and book-shop). However, in the case of your example, co-ordinate, I believe using a hyphen is necessary either for easier readability or to avoid confusion (e.g. re-form NOT reform or re-creation NOT recreation).
    – M.N
    Dec 19, 2016 at 17:03
  • @JohnFeltz You should post that as an answer, because it's correct.
    – user32753
    Dec 19, 2016 at 18:13

1 Answer 1


Compound words in English can be separated by a space (e.g. ice cream), a hyphen (your examples), or nothing (e.g. bestseller).

But, the step in stepbrother, etc. is unrelated to the English word step as in thing you put your foot on to move (from Wikipedia article Stepfamily:)

The earliest recorded use of the prefix step-, in the form steop-, is from an 8th-century glossary of Latin-Old English words meaning "orphan". Steopsunu is given for the Latin word filiaster and steopmoder for nouerca. Similar words recorded later in Old English include stepbairn, stepchild and stepfather. The words are used to denote a connection resulting from the remarriage of a widowed parent and are related to the word ástíeped meaning bereaved, with stepbairn and stepchild occasionally used simply as synonyms for orphan. Words such as stepbrother, stepniece and stepparent appeared much later and do not have any particular connotation of bereavement. Corresponding words in other Germanic languages include: Old High German stiuf- and Old Norse stjúp-.[14]

So this is not really a compound word so much as a separate word or a prefix (e.g. like unknown, pregame, etc.)

  • This answer is a total game-changer. Thanks for having enlightened us (not sarcastic). Dec 20, 2016 at 9:35

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