... is a tree, closely related to the horse chestnut and known scientifically as Aesculus glabra. It's sometimes known as the American buckeye or the fetid buckeye. It's called the 'buckeye' because its nuts look a bit like the eye of a deer.
The buckeye tree is "relatively common" in Ohio (according to the Ohio History Central website). The term 'Buckeye' was already being used to refer to residents of Ohio in 1840, when William Henry Harrison stood as a candidate for the US presidency. Harrison was born in Virginia, but moved to Ohio (from Indiana) following the War of 1812. He was elected to Ohio's State Senate in 1819, and from 1825 to 1828 he represented the state in the US (Federal) Senate.
During his presidential campaign, Harrison's supporters took to carving souvenirs out of buckeye wood. He won the election, but died exactly one month later of a flu-like illness, which was believed at the time to have been brought on by the inclement weather at his inauguration. He was the first US president to die in office, and is still the shortest serving.
In 1953, Ohio's state legislature designated the Ohio buckeye as the official state tree. Ohio has since been commonly known as the Buckeye State, but the nickname does not itself appear to be official.
© Haydn Thompson 2021