- a state in the northeastern central United States: a part of the Midwest. 41,222 sq. mi. (106,765 sq. km). Capital: Columbus. Abbreviations: OH (for use with zip code), O.
- a river formed by the confluence of the Allegheny and Monongahela rivers, flowing southwest from Pittsburgh, Pa., to the Mississippi in southern Illinois. 981 miles (1,580 km) long.
- a state of the central US, in the Midwest on Lake Erie: consists of prairies in the W and the Allegheny plateau in the E, the Ohio River forming the S and most of the E borders. Capital: Columbus. Pop: 11 435 798 (2003 est). Area: 107 044 sq km (41 330 sq miles)
- a river in the eastern US, formed by the confluence of the Allegheny and Monongahela Rivers at Pittsburgh: flows generally W and SW to join the Mississippi at Cairo, Illinois, as its chief E tributary. Length: 1570 km (975 miles)
