A short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead

Wikipedia Word definitions in Wikipedia
Protactinium or protoactinium (former name) is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen , water vapor and inorganic acids . It forms various chemical compounds where protactinium ...

WordNet Word definitions in WordNet
n. a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead [syn: protoactinium , Pa , atomic number 91 ]

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Protactinium \Protactinium\ The radioactive chemical element, of atomic number 91; Atomic symbol Pa; at. wt. of longest-lived isotope, 231 (T1/2 = 32,500 yrs.) Also called brevium, Uranium X2 and UX2.

Wiktionary Word definitions in Wiktionary
n. A chemical element (''symbol'' Pa) with atomic number 91.