蝦夷方言藻汐草

Aca is directly documented for “father” in several dialects, including eastern Shizunai, Urakawa, Samani and Bihoro, and matches アチヤ under 父. Its familiar Saru meaning “uncle” is also attested, but does not invalidate the father reading. Retained corpus contexts include both an uncle and a father from Samani. The modern c spelling accounts for チヤ; the source does not identify a particular regional speaker.