Could anyone explain the differences between "thru" and "through"? Is the difference only in spelling? Is "thru" some sort of slang?

  • 1
    Slang is “very informal usage in vocabulary and idiom that is characteristically more metaphorical, playful, elliptical, vivid, and ephemeral than ordinary language”. Since thru is the exact same word as through, it cannot possibly be considered slang. Spelling is always an approximation anyway; spoken language is primary. Now, if you and your friends used bazinga to mean "through", that would be slang.
    – RegDwigнt
    Commented Nov 20, 2012 at 10:04
  • Related: english.stackexchange.com/q/91685/14666 [now closed]
    – Kris
    Commented Nov 20, 2012 at 12:40
  • en.wikipedia.org/wiki/Simplified_Spelling_Board for how these words came into use (and most were discarded, but some {like thru} lived on)
    – SeanC
    Commented Nov 20, 2012 at 22:13
  • I know this is fairly old topic but food for thought . . . My introduction to "thru" came with my first exposure to the COBOL programming language back in the early 80s. I know many developers that have(had) fallen into the thru habit. I personally never used thru prior to COBOL and now that I'm past COBOL I don't slip too often. I do have to think about it a little.
    – user38330
    Commented Feb 26, 2013 at 22:46

3 Answers 3


I was going to comment that this is General Reference, but actually looking for a reference didn't come up with much.

Merriam-Webster has this...

While never extremely common, tho and thru have a long history of occasional use as spelling variants of though and through. Their greatest popularity occurred in the late 19th and early 20th centuries, when their adoption was advocated by spelling reformers. Their current use occurs chiefly in informal writing (as in personal letters) and in some technical journals.

Wiktionary notes the following, which gives more details on the "technical" usage:

Thru is generally only noted as a preposition (e.g., Monday thru Friday), and seldom as an adjective or adverb (e.g., I'm thru with the vacuuming). Additionally, it is subject to being changed by those who believe it is wrong. It is less used in formal situations, except in cases where brevity is wanted such as roadway signs or date ranges.

It is often noted in professional drafting: "⅝-inch thru hole". Thus noted to save space and simplify annotation on a drawing for fabrication or construction.

This spelling is not used in British English. Also, this usage [that is, "Monday thru Friday"] of the word "through" is very rarely found in British English ("to", "'till" or "until" would be used instead).

So yes, thru is some sort of slang or jargon.

  • 3
    Nice answer; I'm surprised you didn't mention signage, tho. As Grammar Girl says, "people are probably more likely to accept the informal spelling in places where space is extremely tight, such as on road signs..."
    – J.R.
    Commented Nov 20, 2012 at 10:26
  • 2
    @J.R. Wiktionary mentions roadway signs, but I'm from the UK and we don't use the word. Or at least, there's almost always a picture whether we use words or not.
    – Andrew Leach
    Commented Nov 20, 2012 at 10:34
  • Very interesting; I've never seen that symbol before. We just use the "THRU" word here in the U.S. Thanks for sharing that.
    – J.R.
    Commented Nov 20, 2012 at 10:37
  • From what I had earlier checked out, the words (spellings) are not entirely slang or even informal to the extent that it is extensively used in technical writing, apart from a number of instances where well-known authors have used in English literature. I'd say the spellings are correct and formal, only not recommended in regular use.
    – Kris
    Commented Nov 20, 2012 at 12:46

In Strunk & White, E.B. White's answer was:

Do not write nite for night, thru for through, pleez for please, unless you plan to introduce a complete system of simplified spelling and are prepared to take the consequences.

White quotes the original edition, in which Strunk said,

From time to time new forms, mostly simplifications, are introduced by innovators, and either win their place or die of neglect.

White adds, somewhat wistfully,

A word that has taken hold in our century is thruway ... it is a high-speed word for readers who are going sixty.... It is conceivable that because of our thruways, through will eventually become thru -- after many more thousands of miles of travel.

(The Elements of Style, 1979 edition, p. 74-75)

  • 1
    Might be worth mentioning that the New York State Thruway (and its offshoot the New England Thruway) did not set a national trend. More common are turnpike, freeway, expressway, etc. There are slight variations in meaning (in California, an expressway has less restricted access than a freeway), not to mention names that get left behind: there are no longer tolls on several so-called turnpikes! Commented Nov 20, 2012 at 20:02
  • 1
    Agreed, @AndrewLazarus, I searched for "thruway" in Google (US) and the top ten pages of links were all for the New York State Thruway (or stores or hotels on that thruway). The sole exception was the "California Thruway," which seems to be a marketing ploy of the train system, Amtrak. White may rest easier that "thru" has not received any more than a toehold.
    – rajah9
    Commented Nov 21, 2012 at 14:36
  • Every time I cross the San Francisco Bay Bridge, I pass a sign that says, "THRU TRAFFIC MERGE LEFT." I imagine there are lots of similar signs round about. My impression is that the short form "THRU" is designed to be more readily comprehensible to drivers (and passengers) who may be passing the sign at high speed and who may not instantly recognize the character string "THROUGH." The simplifying impulse here is not altogether unlike the one that led fire marshals to champion replacing "INFLAMMABLE" with "FLAMMABLE" on canisters of combustible gas.
    – Sven Yargs
    Commented Feb 27, 2013 at 0:10
  • Yes, Sven, Strunk & White agree with you. On "flammable," they say it's "An oddity, chiefly useful in saving lives."
    – rajah9
    Commented Feb 27, 2013 at 15:17

Yes, “thru” is incorrect, but it's shorter to write. Just like “u” for “you” etc.

That's all.

Seems I was not absolutely right; see Andrew's answer. Sorry.

  • That's usually not all :) We are supposed to check and provide citation in support of our answers, aren't we?
    – Kris
    Commented Nov 20, 2012 at 12:42
  • 2
    @Kris Yes, so I wonder who upvoted this...
    – Mr Lister
    Commented Nov 20, 2012 at 12:51

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