radioactive element discovered in 1899; see actino- "pertaining to rays" + chemical suffix -ium. It emits beta rays. The name was given earlier to a supposed new element (1881).
acrostic
acrylic
act
Actaeon
acting
actinium
actino-
action
actionable
activate
activation
)window.location='https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=byronic106@yahoo.com&lc=US&item_name=Donation+to +Help+Keep+Etymonline+Free+and+Open&no_note=0&cn=&curency_code=USD&bn=PP-DonationsBF:btn_donateCC_LG.gif:NonHosted'){kind=link}