RE: "Supposedly, the -ough in every word sounds different..." Is that really the case, or is that just your assumption? (It could be that slough was added, not because it has a different sound than the rest of the words in the sentence, but because, unlike the other -ough words in the sentence, it has more than one possible pronunciation.)

This example both has a recording of the pronunciations and highlights in bold text the 8 different sounds it claims. 'Slough' isn't bolded, so not thought by those authors to be an additional pronunciation. englishclub.com/ref/esl/Power_of_7/7_Ways_to_Say_ough__2924.‌​htm

@Spagirl Hit the nail on the head IMO

There are many regions of the U.S. where the pronunciation is sloo. Rhymes with through.

I deleted my initial comment but as the link by @Spagirl shows, the pronunciation of slough is not meant to provide a unique pronunciation, different from all the other -ough words. It's probably included because it can be pronounced three different ways.

Thanks all for the responses. That does seem to clear my doubt. Just before I call it a case closed, there is one image that I saw the earliest (and on a few other websites) and it does seem to imply that slough bears a unique pronunciation. Can anyone confirm with me that I should ignore this image? s-media-cache-ak0.pinimg.com/736x/b1/6e/2f/…

Miss Joey: I don't think you should ignore that image – but you might want to add it to an edited version of your question.

Sure @J.R., an edit has been made.

According to the page How to pronounce 'Slough', -ough has nine pronunciations, and slough does not offer a tenth. So I dunno what pronunciation that chart is meant to represent, unless it's some dialect I'm not familiar with (which could be possible).

@MissJoey What pronunciation are you attributing to 'lough'? As an Irish-Gaelic loan word a majority of speakers of Standard English are likely to pronounce it 'lock', while those more familiar will pronounce it much as Scots say 'loch'. The fact remains that its a loan word which many english speakers will never encounter.

slough is two different words, one pronounced like slew and the other pronounced like sluff.

@Drew that's not the point; whichever word slough you choose, there is already a word in the chart (or the originally posted sentence) that rhymes with it (through, rough, plough).

@Clare I would not personally rely on the last two procunciations on that link. Poughkeepsie is a borrow-in from Wappinger en.wikipedia.org/wiki/Wappinger and Coughlin is again Irish-Gaelic and not pronounced the same there as in North-America. Even in NA there are several pronunciations. I've known people in England pronounce it 'Coch-lin'. webcache.googleusercontent.com/… On the whole, MissJoey I'd probably omit loan-words or mention as an aside.

@Spagirl, MissJoey The Wikipedia entry on ough offers 9 AmE pronunciations and 10 BrE pronunciations (Scottish lough included), and offers only three pronunciations of slough; it also mentions further pronunciations of -ough in proper nouns.

Never seen hiccoughing in all my born days. To think that I had always thought it was: hiccuping. Well, that's one BrE and AmE that beat me. :)

I think @Spagirl should turn her original comment into an answer. I would upvote it.

Then there's always sough, which is (or can be) pronounced /suːx/ in Scotland, and elsewhere quite a few other ways, @Spagirl et al.