Pronunciation: (dī'u-fōn"),[key] —n. 1. a foghorn producing a low-pitched, penetrating signal of two tones.
2. Phonet. a. a phoneme in one dialect corresponding to a similar but phonetically different phoneme in a related dialect.
b. a group of sounds comprising all the phonetically different dialectal variants of a given phoneme in a language: The broad a and flat a of “half ” are members of a single diaphone.