(also Uda), a river in Chernigov and Poltava oblasts, Ukrainian SSR; a right tributary of the Sula River of the Dnieper River basin. The Udai is 327 km long and drains an area of 7,030 sq km. It rises and flows in the Dnieper Lowland. It is fed mainly by snow. The mean flow rate 39 km from the mouth is 9.4 cu m per sec. The river freezes between November and early January and opens up between March and mid-April. The cities of Priluki and Piriatin are situated on the river.