Diaphoneme

A diaphoneme is an abstract phonological unit that identifies a correspondence between related sounds of two or more varieties of a language or language cluster. For example, the vowel that constitutes the English word eye is pronounced differently depending on dialect ([aɪ̯] or [ʌɪ̯] in RP and General American, [ae̯] or [əi̯] in Scottish English, [ɑɪ̯] in Australian English, [ɔɪ̯] in Irish English, [aː] in South African English, and [aː] or [əi̯] in Southern American English, etc.) but, in the appropriate context, all of these variants are perceived by speakers as equivalent, and thus constitute a single diaphoneme. The word diaphone was originally used with the same meaning, but was later repurposed to refer to any of the particular variants, making the relationship between diaphoneme and diaphone analogous to that between phoneme and allophone.