Hyphenation Rules for 35 Prefixes (and 1 Suffix)

By Mark Nichol

There was a time when prefixes were routinely attached to root words with hyphens, but that time has, for the most part, passed. Now, hyphens are the exception, as detailed in the following list, which also provides simple definitions.

ante (before): closed
anti (against): closed except before a proper noun or a word starting with i
bi (twice, two): closed
bio (life): closed
co (with): generally closed; exceptions include co-op and co-opt
counter (opposite): closed
cyber (computer): closed
extra (beyond): closed except before a word starting with a
hyper (above, beyond, excessively): closed
infra (below, within): closed
inter (between): closed
intra (between, during, within): closed
mega (large): closed except before a word starting with a
meta (behind, beyond, changed, later): closed except before a word starting with a
micro (small): closed
mid (middle of): closed except with numbers, proper nouns, and terms of more than one word
mini (short, small): closed
multi (many): closed except before a word starting with i
neo (new): closed except with select proper nouns; check dictionary (lowercase and hyphenate if attached to proper name and term is not in dictionary)
non (not): closed except if attached to hyphenated phrase (use en dash instead of hyphen if attached to term of more than one word)
over (above): closed
post (after): closed except before a proper noun (use en dash instead of hyphen if attached to term of more than one word)
pre (before): closed except before a proper noun (sometimes capitalized in a proper noun—check dictionary; use en dash instead of hyphen if attached to term of more than one word)
pro (for): closed except in pro-life and before a proper noun
proto (beginning, first): closed
pseudo (false): closed except before a proper noun
re (again, back): closed except to avoid confusion as in resign (quit) versus re-sign (sign again)
semi (half of, partly, partially): closed except before a proper noun or a word starting with i
sub (almost, beneath, below, less than): closed
super (beyond, superior): closed
supra (beyond): closed
trans (across, beyond, through): closed
ultra (beyond): closed
un (not): closed except before a proper noun or a word starting with u
under (below): closed

fold (multiplied by): closed except with numerals or with spelled-out numbers that are hyphenated

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9 Responses to “Hyphenation Rules for 35 Prefixes (and 1 Suffix)”

  • Dale A. Wood

    Oh, by the way, “reform” and “re-form” are two different words, just like “resign” and “re-sign”.

  • Dale A. Wood

    Just today, I was reading an article in the Wikipedia that used inconsistent spelling scattered all the way through concerning “counterattack” and “antiaircraft”, and I imagine that those British/ European/ Australian writers would have difficulty with these, too: counterclaim, counterclockwise, counterweight, counterrotating, counterintelligence, counterrevolutionary, and counter-counterintelligence.

  • Dale A. Wood

    ALL of the prefixes of the International System of Units (the S.I. from its French abbreviation) are closed. The common ones of these include the following: kilo, mega, giga, tera, centi, milli, micro, and nano; and some of the less-usual ones include pico, deci, deka, and hecto – as in picometer, picofarad, dekagram, dekaliter, and hectogram.
    The words dekagram, dekaliter, decibel, and deciliter were even in my spellchecker. “Deciliter” sees some use in the medical and dental fields, and “decibel” is mostly in the province of engineers and audio technicians.
    Sometimes the new word is contacted as in the words hectare, kilampere, megampere, kilohm, megohm, and gigohm. “milliampere” and “microampere” might be considered to be difficult, but there they are – very commonly used in electronics, and sometimes in medicine.

  • Dale A. Wood

    Quoting: “non (not): closed except if attached to hyphenated phrase (use en dash instead of hyphen if attached to term of more than one word)”.
    EXCEPTIONS: non-Catholic, non-Protestant, non-Jewish, non-British, non-Chinese, non-Communist, non-Fascist, non-notable, non-notice.
    “Because of your non-noticing that the hatchback was open, you are responsible for the child’s falling out!”

  • Dale A. Wood

    The prefixed “mini”, “midi”, and “maxi” are all closed, regardless of what some Brits, etc., might think. These words include miniskirt, midiskirt”, “maxiskirt”, “minimax”, “maxishoes”, “minibrain”, “microbrain”, and “maxibrain”, two of which my spellchecker does not like. Well, pfui on it!
    Minicircuit, minicomputer, microprocessor, microcomputer, microcircuit, microwave.

  • Dale A. Wood

    In some cases of adding prefixes, the words become contracted, such as in “bi-injection, with becomes “bijection”.
    Also, at least in the language of aerospace, reenter and reentry are written in close form.
    My spellchecker says that “reestablish” is acceptable, but I prefer “re-establish”. Aircraft can be “reengined”, or should it be “re-engined”? Cases of this include replacing turbojets with turbofans, which has been done by the U.S. Air Force in the cases of the KC-135 Stratotanker and the B-52 Stratofortress. There is another prefix for you – “strato”, as in “stratosphere” and “stratocumulus”. An automobile can be reengined by replacing a V-6 with a V-8, and the P-51 Mustang was reengined by replacing the Allison engine of the P-51A with the great, supercharged Rolls Royce Merlin engine of the P-51B and all succeeding versions. This was a stroke of genius, especially considering how much this improved the high-altitude performance of the P-51B, P-51D, etc., and also improving their fuel efficiency. (These Rolls Royce were manufactured by the Packard Motor Company in Detroit.)
    Other good words include “reengineer”,
    “reengage”, “reemerge”, but the British like to hyphenate these.

  • Dale A. Wood

    Regardless of any other considerations:
    “un (not): closed except before a proper noun or a word starting with u”, “unusual” and “unused” have closed prefixes.
    I feel so strongly about this that I am tempted to write “irregardless” !
    I can’t think of any other cases, except in possible “un-uncle”, for a man who is not your uncle. There are also geographical named like “Unalaska”, but those came from the languages of the native peoples of the areas.
    “Un-unified” is not needed because we have the word “nonunified” already.

  • Dale A. Wood

    Amazing, wonderful! Just the way that I would put it, and only if we could convince the Brits, the Aussies, and the South Africans to go along with it all!
    Especially considering the words “antidisestablishmentarianism”, “antimissile missile”, and “antichlorgenic”. This also brings up another nonhyphenated prefix “dis”, and in disinterested, disabled, dissimilar, disassemble, and disinformation!

  • Anne-Marie Shaffer

    What? No examples?

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