Generally, double consonants are not pronounced distinctly in English, unless they are part of different syllables and the emphasis is on the second syllable.
A word like dissatisfied is formed by adding a prefix dis- to the word satisfied. It starts off with two s in separate syllables, and can be pronounced like that- one at the end of the first syllable, one at the end of the second syllable.
A word like irregular is formed by adding a prefix in- to the word regular. The n-r combination is difficult to say, so we replace the n by another r. The same thing happens with the letter l, so in + licit becomes illicit. According to Cambridge Dictionary, the first l is not pronounced, likewise with in + modest. Note that this conversion only happens with word that passed through medieval latin: more modern words like inroad (1540), inlay (16th C) and inline (1913) are unaffected.
The same kind of conversion happens in arabic for sun letters (il+r -> irr). In arabic double consonants are always clearly pronounced, and this applies to sun letter conversions too.
In a non-rhotic dialects there is an identifiable reaason for not pronouncing the first r, because in non-rhotic dialects (England english, for example) an r followed by a consonant is not pronounced.
In rhotic dialects such as US english, the pronunciation of the n-become-r is, according to Merriam-Webster, optional.
I am a native of England (non-rhotic) and I do not pronounce it as a double r. I can and do double the r when speaking arabic, so I do understand the difference. Other natives of England do not pronounce the double r. If I heard somebody pronounce it with a double r, I would assume that they were foreign. I believe that I have heard natives of Scotland (rhotic) pronouncing it with a double r. I cannot comment on US english.
Here are recordings of me saying irregular and erectile:
And here I say irregular again, pronouncing the two r's separately.
𝑇𝐿;𝐷𝑅
In General American English, don't is pronounced /doʊnt/ while in Southern Standard British English, it's pronounced /dəʊnt/.
In don't you, the /t/ of don't and /j/ of you coalesce to /tʃ/. The process is called assimilation.
𝐸𝑥𝑝𝑙𝑎𝑛𝑎𝑡𝑖𝑜𝑛
Assimilation makes nearby sounds more similar to each other. The kind of assimilation in don't you is called coalescent assimilation.
When /j/ comes right after /t/, there's a tendency to assimilate them to /t͡ʃ/. The /t/ is normally articulated at the ridge right behind the top teeth (alveolar ridge), but when it comes before a /j/ (which is articulated further back in the mouth—at the hard palate), it's usually pronounced /t͡ʃ/. What happens here is that the /t/ is articulated further back in the mouth in anticipation of the following /j/, so it becomes /t͡ʃ/ i.e. they coalesce to /t͡ʃ/.
The following sounds often coalesce:
- /t/ and /j/ coalesce to /t͡ʃ/ (as in posthumous)
- /d/ and /j/ coalesce to /d͡ʒ/ (as in education)
- /s/ and /j/ coalesce to /ʃ/ (bless you is sometimes pronounced bleshoo)
- /z/ and /j/ coalesce to /ʒ/ (as in vision)
You might have noticed that in informal situations (mostly in chatting platforms), most people write contractions such as dontcha, whatcha, gotcha etc. These are the phonetic spellings of the assimilated forms.
- dontcha → don't + you
- whatcha → what + you
- gotcha → got + you
- betcha → bet + you
Similarly, 'did you' is often pronounced as /dɪdʒjuː/ because /d/ and /j/ assimilate to /d͡ʒ/.
I wonder is this something specific to American accent?
No. It's not restricted to American English.
Best Answer
TLDR
The pronunciation of 'iron' in standard varieties of English is EYE-URN (BrE: /'aɪən/, AmE: /'aɪrn/) and not EYE-RUN (which is also a common pronunciation of 'iron' in some varieties of English) because of a very common process called Metathesis. It's defined as the transposition/rearrangement of letters, syllables or phonemes (sounds) in a word.
Explanation
There are some other words that show the same change; 'wasp' used to be waps, 'bird' used to be brid and 'horse' used to be hros, but they've changed over time. Why is that?
It's because of a very common process called Metathesis. /'aɪən/ is the metathesised version of (/'aɪrən/). 'Iron' commonly used to be pronounced the way it's spelt (/'aɪrən/), but due to metathesis, its pronunciation became EYE-URN (/'aɪən/). Other words such as horse, bird, third etc., reflect the change in spelling; however, 'iron' doesn't reflect that change probably because metathesis applied to it after the spelling was standardised.
Metathesis:
Metathesis is defined as ’the transposition/rearrangement of letters, syllables or phonemes (sounds) in a word’.
Examples:
{Historical Metathesis}
'mix' being pronounced /mɪsk/ rather than /mɪks/ [transposition of k and s]
'desk' being pronounced /dɛks/ rather than /dɛsk/ [transposition of k and s]
'modern' being pronounced /'mɒdɹən/ instead of /ˈmɒd(ə)n/ (US: /ˈmɑː.dɚn/)
'pattern' being pronounced /pætɹən/ instead of /ˈpæt.ən/ (US: /ˈpæɾ.ɚn/)
Another famous example from Shakespeare's 'The Tempest' is the figure of Caliban whose name originates from a phonological metathesis of /n/ and /l/ in 'cannibal'. [ThoughtCo]
/r/-metathesis
Words having /r/ + vowel sequences are more susceptible to metathesis than others. According to A grammar of Old English Phonology by Richard Hogg, ‘R-metathesis normally occurs when /r/ is followed by a short vowel and a dental or alveolar consonant, usually /n/ or /s/’.
'Iron' is an example of /r/-metathesis. It was probably pronounced /'aɪrən/ (EYE-RUN) at one point, but it got metathesised to /'aɪərn/ (EYE-URN). However, the spelling remained unaffected.
Other examples of metathesis of /r/ include:
The silent R in 'iron' in BrE
The reason why the r in 'iron' is absent in British English is because the r is followed by a consonant now (followed by /n/ in /'aɪərn/) and British English is non-rhotic, meaning the r is only pronounced when followed by a vowel. The same thing happened to 'bird', 'horse' and 'third' too (i.e. the r is followed by a consonant, so it's silent).
There are different types of metathesis, 'colonel' (pronounced KE(R)-NUHL /'kɜː(r)nl̩/) can also be said to be a product of metathesis. (See this answer on ELU for the spelling and pronunciation of 'colonel')
According to Wikipedia, the reason for ‘common speech errors’ is also metathesis.
Examples include:
References: