I've been receiving emails at work inquiring about registering our key fobs. This is slightly disturbing to me as I've always called it a key thob. An internet search for thob tells me I really mean fob, but if I force it to search for thob instead, it finds plenty of results (1.1 million for thob compared to 7.7 for fob).

Is thob considered incorrect? Is it recognized? Is it obsolete? Or are some people just making up words by calling it a thob?

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    @glowcoder: When I Googled quotated "key fob" it first claimed About 5410 results, but on scrolling through I find there are actually only 484. I can only assume it's something to do with mis-hearing, but it's far more results than I would have expected. So - here's my apology. I'm voting to reopen in case someone can explain why this error happens. – FumbleFingers Nov 16 '11 at 23:39
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    btw - I expect the fact that three of your coworkers say "thob" is because you all work together, and pick up the error from each other. So it's not "statistically" significant. – FumbleFingers Nov 16 '11 at 23:41
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    Paging through the results finds 620 results for "key fob" vs. 491 for "key thob", with similar pages omitted. If you tell it to return all pages, both searches go to the maximum 100 pages without running out of results. I think we can safely say that this is not a localized mispronunciation. – Marthaª Nov 17 '11 at 0:20
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    @JasperLoy: Oh, there's no question that "fob" is correct and "thob" is a misspelling/mispronunciation. The question is, where does "thob" come from, and why is it (apparently) so common? – Marthaª Nov 17 '11 at 1:28
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    Note that searches for key thob without the quotes find mostly pages with both "key" and "thob" but not together. The first ten pages are misleading. – Charles Nov 17 '11 at 15:41

As discussed above, this is clearly an error. However, it is an interesting error, which is driven by several different things:

  1. The word fob is very rare, and is essentially unused outside of this expression and the idiomatic verb to fob off. Therefore it's not surprising that some people mis-acquire the word, since they have so few chances to correct themselves.
  2. The sounds for th and f are acoustically very similar, and it is not difficult to mishear f as th. For a demonstration of this, see page 13 of this paper showing nearly identical frequency graphs for f and th [θ].
  3. Because of #2, there are several English dialects where f is a frequent substitution for th, e.g. think is pronounced as fink. Speakers of these dialects have extra trouble knowing when to write f and when to write th, so many of the errors that you can find may be from people for whom fob and thob are actually pronounced identically. These people probably say fob, but mistakenly believe that the proper spelling is "thob".
  4. Finally, the characteristic errors of the dialects in #3 prompt a hyper-correction from some people, causing them to "correct" f back to th in places where the f was actually correct. So some of the instances of thob may be due to people thinking that fob is a mistake, and that thob is the correct form.
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    Another point is that the uses of the word in "key fob" and "fob off" appear completely unrelated (and have etymologically different origins). So even if somebody knows the right spelling for one of them, it doesn't help them to spell the other. Surprisingly, Google finds extremely few instances of "thob off". – Peter Shor Nov 17 '11 at 14:19

I get about 1000 times as many results on Google for "key fob" as "key thob". Google n-grams doesn't list a single occurrence of key thob.

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I've never heard it used in any context, historical or otherwise; I suspect it's a mistake.

  • Searching for 'key thob' yields 1.1 million results. Link: google.com/search?q=key+thob&nfpr=1 Searching for 'key fob' yields 7.7 million results. Link: google.com/search?q=key+fob - That's not 7 times as many, not 1000 times. The lack of it being used in a book may simply mean whenever it's come up during editing it's been decided to use fob. That doesn't speak for the social trend though, only the published trend. – corsiKa Nov 16 '11 at 23:09
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    @glowcoder: the number of results reported by Google on the first page is wildly inaccurate. The actual number could be several orders of magnitude smaller or larger (though it's generally smaller). You cannot draw any conclusions based on that number. – Marthaª Nov 17 '11 at 0:12
  • @martha Thanks for that information. I'll keep that in mind in the future! – corsiKa Nov 17 '11 at 0:32
  • Also note that I used quotes which reduces the number of results in both cases. – Charles Nov 17 '11 at 14:20
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    Google N-Grams only looks at published sources, which are vastly more likely to have the correct spelling. Ngrams are useless for catching this sort of mistake in the wild. – JSBձոգչ Nov 17 '11 at 15:19

Fob is correct. It comes from the term for a watch fob, a dangle or ornament that hung from your watch chain. Key fob, a device or ornament that hung from your car or door key, came to mean key chain. Then car manufacturers started using it for the auto-lock device that hangs from your keychain. The security key fob looks like the car start device, so people called it a key fob, especially as many people used to hang it from their keychains.

As for the f vs th sound, my husband used to pronounce the city of Philadelphia as Philadelthia, as he could not discern the difference in sound. So it happens in other words as well.

  • My dad says "Philadelthia" as well. – sumelic Sep 29 '15 at 21:17

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