Iron appears to be mispronounced by almost all non-native speakers of English. I don’t remember learning the correct pronunciation in school and most people presumably never notice that there is a right and a wrong pronunciation. I have heard numerous, highly-trained scientists with otherwise excellent English skills who spend their day working with iron consistently mispronounce this four-letter word. Keep reading if you want to find out whether you know the correct pronunciation.
Getting it right
The widely used but incorrect pronunciation is closely related to that of ironic. You can hear me pronounce iron incorrectly here:
The phonetic spelling of ironic in British English is [aɪˈrɒnɪk], whereas in American English it is [aɪˈrɑːnɪk], listen here. In both British and American English, the sound [aɪ] for the first letter in ironic is followed by an [r]. However, it is a mistake to assume that the same should be true for iron. Instead, the correct pronunciation is [ˈaɪən] in British English, and [ˈaɪərn] in American English, listen here. The crucial difference is that for iron, the sound [aɪ] is not followed by an [r]. In fact, there is no [r] sound at all in the British pronunciation, whereas the [r] in the American pronunciation comes after the [ə]. The origin of the pronunciation of iron is sometimes argued to be related to the German word eisern (meaning: made of iron), which rhymes to some extent with the correct pronunciation of iron. By the way, the pronunciation of the other chemical elements is discussed here.
The mistake in action
The incorrect pronunciation can be heard in reference to the chemical element iron, and in every-day terms such as ironing or Iron Man (sports or movies). A good example is this German trailer:
I have even heard several people working in the magnificent Flatiron Building in New York City make the same mistake. Because of the challenges involved, I believe that the pronunciation of iron is an excellent test to distinguish between native and non-native speakers.
Iron and environment
Finally, let us consider the word environment. According to the dictionaries, the standard pronunciation is [ɪnˈvaɪrənmənt], listen here. However, after hearing native speakers use other pronunciations on several occasions, I consulted the Longman Pronunciation Dictionary, which offers several other (less widely used) pronunciations. Most notably, some people pronounce ‘iron’ in environment using the American pronunciation of the word iron, so that the complete pronunciation becomes [ɪnˈvaɪərənmənt]. The British version, [ˈaɪən], is apparently not used, so that there is always an [r] in environment. Another variation is to drop the middle n, that is, [ɪnˈvaɪrəmənt].