How do you say 'polygon'? Traditionally it was [ˈpɒlɪgən] in British English. But increasingly, according to Lindsay (2019), it is becoming [ˈpɒlɪgɒn], with a full vowel in the final syllable rather than a schwa. Why is this change taking place?
The first factor affecting its pronunciation is spelling pronunciation: 'o' gets pronounced as [ɒ]. But in this case, there is another factor: American pronunciation. In America, there was always a full vowel in the final syllable, so it was [ˈpɑːlɪgɑːn]. So the change in British pronunciation reflects American influence.
Traditionally, in British English, speakers were averse to having a secondary stress after the primary, so 'secondary' was [ˈsekəndərɪ], with three unstressed final syllables, and similarly 'secretary' was [ˈsekrətərɪ]. In fact, there could even be four unstressed final syllables, as in 'voluntarily' [ˈvɒləntərəlɪ] and 'necessarily' [ˈnesəsərəlɪ].
But American English does not have this constraint, so these words have a secondary stress (or at least a full vowel) in the third syllable: [ˈsekənˌderɪ], [ˈsekrəˌterɪ], etc. And this pattern seems to be becoming more common in British pronunciation as well.
So perhaps the change in the pronunciation of 'polygon' (also 'pentagon' and 'hexagon') reflects the growing influence of American English and is not just spelling pronunciation.
As with 'mosquito', which I discussed in my previous post, I am pretty sure that all my Brunei students have a full vowel in the third syllable of these words, so in this respect Brunei English is more progressive in the ways English is changing than British English.