a radioactive chemical element, an alkali metal, existing in minute amounts in nature as a decay product of actinium: symbol, Fr; at. no., 87
See francium in American Heritage Dictionary 4
(frănˈsē-əm)
noun Symbol Fr
An extremely unstable radioactive element of the alkali metals, produced artificially from actinium or thorium, having approximately 19 isotopes, the most stable of which is Fr 223 with a half-life of 21 minutes. Atomic number 87; valence 1. See Table at element.