Noun.  a radioactive, metallic chemical element (''symbol'': Ac) with an atomic number of 89; found in uranium ores.

This is an unmodified, but possibly outdated, definition from Wiktionary and used here under the Creative Commons license. Wiktionary is a great resource. If you like it too, please donate to Wikimedia.

This entry was last updated on RefTopia from its source on 3/20/2012.