I've been told that in American English, sometimes words ending in -ough are written -u: for example thru instead of through.

Is this correct English, or is it simply a common error?
If it is correct, what are the rules for this spelling?

  • 2
    There's another -ough class that wouldn't be shortened to -u -- place names ending in -borough, often shortened to -boro. (It's amusing to see at times, by the side of the road, adjacent signs with the different spellings; one such pair is in North Attleboro/o, Massachusetts.) Commented Feb 3, 2013 at 21:30

5 Answers 5


"Thru" is correct (however very informal, not a very good idea, and only used when space is at a real premium — e.g. road signs, technical drawings) English, but -u is not a shortened way of -ough except in words that derivate from through (e.g. breakthrough).

From memory, I can recall although, enough etc. where -ough can't be replaced by -u (althu, enu etc.), since in those words -ough doesn't have a /u/ sound. (However, although can be shortened to altho, as noted in a comment — however, Wiktionary and other dictionaries register it, noting that it's quite informal.)

  • 11
    N.b.: Merriam-Webster calls it an "informal simplification" so it should be avoided in any formal writing. I would only ever use it for texts.
    – Ryan Haber
    Commented Jan 23, 2013 at 21:42
  • 6
    +1 The reason why though and enough can't be written *thu and *enu is obviously that they are not pronounced /u/, unlike through. I can't think of any other very common words ending on -ough and pronounced -/u/. // You might want to stress a little more that spelling thru is a really bad idea nearly everywhere, including most of the Internet, e-mails, school, etc. People may think, "oh, I'm not writing to my professor, so it's informal", whereas "informal" in linguistics is sometimes a bit of a euphemism for what others call "bad spelling, ignorant, wrong", as it is in this case.
    – Cerberus
    Commented Jan 24, 2013 at 2:38
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    "Although" is shortened to "altho."
    – Flimzy
    Commented Jan 24, 2013 at 19:19
  • 2
    I've never seen altho. Bad recommendation. VERY informal, only for internet chat, I would say. Commented Feb 3, 2013 at 19:19
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    No, I’m afraid this is the wrong answer: thru is not an admissible substitute for through in Standard English.
    – tchrist
    Commented Feb 10, 2013 at 1:36

As a speaker of American English, I would understand what was meant by thru for through, but I would find it very informal. The Oxford Dictionary entry supports this, saying that it is:

chiefly North American; informal spelling of through.

The rule, however, isn't that words ending in -ough are shortened to -u, but instead in very informal writing the last vowel sound of a word is used instead of the proper ending. This gives through → thru because of the final "oo" sound, but also abbreviated forms though → tho or although → altho because they end in "oh" (as in "cold").


Shortenings you are more or less likely to see for "-ough" (most are, as previously noted, considered at best very informal and at worst a severe case of bad spelling):

  1. through, breakthrough → u
  2. cough → off
  3. enough → uf
  4. tough, rough, slough (verb) → uff
  5. slough (noun) → ew/ue
  6. borough, though, although, thorough → o
  7. furlough → ow (as in "low")
  8. plough → ow (as in "how"; "plow" is now the common spelling)
  9. hiccough → up ("hiccup" is now the common spelling)

A couple of "ough" words are never shortened due to either the word's low frequency, variability of pronunciation, or to any replacement being a collision with another word: sough, dough, brough, bough, trough.


Thru is a very informal spelling that is never used in print or school. Through is probably not the best way to spell it in textspeak, because textspeak avoids long traditional spellings.

But in formal and semi-formal (anything but the most informal) you should avoid using such simplifications unless you are in a place where you've seen others use it. For example, if you use thru here at ELL, it won't be considered a misspelling but will definitely be considered too informal.


It is worth noting that "thru" is a valid (and indeed, common) spelling only in American English. In British English it is an incorrect spelling, and students in Britain would expect to lose marks in exams for using it.

  • 2
    Students in America would have similar expectations, at least in my experience.
    – user230
    Commented Feb 3, 2013 at 9:23
  • Not sure what you mean by "valid" and "incorrect" here. Macmillan has this note: an informal way of writing 'through'. This is sometimes used in newspapers and very informal American writing, but it is not generally accepted in British English. In other words, U.S. teachers wouldn't consider this variant a correct way to spell it on a test, either, even if one might see it on a street sign.
    – J.R.
    Commented Feb 3, 2013 at 18:57
  • By invalid, I mean that students writing "thru" for "through" in England is not normal shorthand, and would be considered a form of illiteracy in British English, rather than an acceptable abbreviation in American English; the only exceptions being for "texting" (where artificial abbreviations reign supreme) or in imported phrases such as a "Drive-Thru".
    – Matt
    Commented Feb 4, 2013 at 19:41
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    It is not admissible in American writing, either, and more than lite is.
    – tchrist
    Commented Feb 10, 2013 at 1:38
  • But thru and lite are very common in American corporate branding. Using these forms in British English only occurs when one is trying to affect an Americanism or make fun of that habit.
    – toandfro
    Commented Jan 12, 2014 at 23:42

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