Penelitian ini bertujuan mengkaji hubungan kekerabatan, waktu pisah, pasangan korespondensi fonemis, dan perubahan bunyi dalam bahasa Aceh dan bahasa Gayo. Penelitian ini menggunakan metode penelitian kombinasi (pendekatan kuantitatif dan kualitatif) dengan menerapkan teknik leksikostatistik dan glotokronologi. Secara kuantitatif diperoleh hubungan kekerabatan antara bahasa Aceh dan bahasa Gayo adalah 43% yang dapat dikelompokkan dalam kelompok keluarga. Hasil perhitungan glotokronologi, bahasa Aceh dan bahasa Gayo merupakan bahasa tunggal diperkirakan antara 1.768 – 2.000 tahun yang lalu dan kemudian berpisah dari bahasa protonya antara 254 SM – 22 SM (dihitung dari tahun 2022). Hasil penelitian secara kualitatif menunjukkan adanya korespondensi fonemis antara bahasa Aceh dan bahasa Gayo ditemukan 13 Pasangan yaitu fonem /ɯ/~/a/, /ɯ/~/ə/, /ɛ/~/u/, /e/~/i/, /ə/~/e/, /o/~/u/, /o/~/ͻ/, /a/~/ə/, /a/~/ə/, /ͻ/~/u/, /a/~/e/, /a/~/Ø/, /i/~/l/, dan /h/~/ Ø/. Selain itu, juga ditemukan perubahan bunyi pada PAN dalam bahasa Aceh dan bahasa Gayo meliputi perubahan bunyi metatesis, aferesis, sinkope, apokope, protesis, epentesis, paragog, lenisi, dan fortisi.

This study investigates the percentage of kinship level, separation time, and phonemic correspondence among Acehnese, Devayan, Sigulai, and Jamee languages by applying theories from Keraf (1996) and Crowley & Bowern (2010). Data was collected using interviewing, recording, listening, and note-taking techniques. Data analysis applied lexicostatistics and glottochronology techniques. The study's results indicated that Acehnese, Devayan, Sigulai, and Jamee languages were related. Based on the results of lexicostatistical calculations, it is known that the Acehnese-Devayan language, Acehnese-Jamee language, Devayan-Sigulai language, Devayan-Jamee language, and Sigulai-Jamee language can be grouped into (family) while Acehnese-Sigulai language is at the (stock) level. Acehnese and Devayan languages were a single language estimated between 2,054-2,458 years ago. Acehnese and Sigulai languages were a single language around 3,169-3,420 years ago, Acehnese and Jamee languages were a single language in 1,836 -2,206 years ago, Devayan and Sigulai languages were a single language in 1945 -2283 years ago, Devayan and Jamee were a single language in 2114-2,316 years ago, Sigulai and Jamee were a single language between 2,010-2.404 years ago. In addition, phonemic correspondences were also found within the four languages.