This was originally posted to the blog that I had while I was a student at University of Michigan, on August 27, 1998.
If a homophone is what you get when you have two different words that sound the same, then I imagine a heterophone is what you get when you have two different words that sound different. Naturally, most words sound different from one another, so most words are heterophones.
What would a biphone be? A biphone would have to be a word that can sound two different ways: one way that sounds the same as another word, and another way that sounds different from other words. Like bisexuals, a biphone can go both ways.
I can only think of one biphone: “route”.
The word “route” can be a homophone, because it can be pronounced the same as “root”.
However, “route” can also be pronounced so that it rhymes with “pout”. When it is pronounced that way, there is no other word that sounds like it… so it is a heterophone in that pronunciation.
Therefore, “route” is a biphone.
Are there any other biphones out there?