|prōd.+ noun
or pro·to·actinium |prōd.(ˌ)ō+
Etymology: New Latin, from prot- + actinium
: a shiny metallic radioelement of relatively short life that is formed in nature by loss of an alpha-particle and a beta-particle from uranium 235, that disintegrates into actinium and ultimately into lead, and that is pentavalent in compounds and shows close chemical resemblance to tantalum but differs in that its pentoxide is exclusively basic with no acidic characteristics — sumbol Pa ; see actinium series , uranium series ; element table