otsu

1. not comparablehuman sciencesIn Old Japanese, one of two sets of vowels of uncertain pronunciation which fell together in modern Japanese.

   Later—during the ninth century—the kō and otsu groups did come to be used interchangeably.

   1991, Christopher Seeley, A History of Writing in Japan

   1 more example

   He rejects the claim of Matsumoto (1984) that the kô and otsu -o- vowels are in complementary distribution, and therefore these two vowels are allophones of a single vowel.

   2001, John R. Bentley, A Descriptive Grammar of Early Old Japanese Prose

alternative Ōtsu

1. The capital city of Shiga Prefecture, Japan.