What is "sequanium"

n. (context obsolete English) (non-gloss definition: An early name for the element neptunium, based on a discredited claim of discovery)

Sequanium was the proposed name for a new element found by the Romanian physicist Horia Hulubei in 1939. The name derived from the Latin word Sequana for the river Seine running through Paris where Hulubei worked at that time.

Hulubei thought he had discovered element 93 in a tantalite sample from the French region Haute-Vienne. Later it was proven that element 93 is not present in the natural environment and is only produced in nuclear reactions. The element 93 was synthesised in 1940 and named neptunium.