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actin
actin-
actinal
acting
actinian
actinic
actinide
actinism
actinium
actino-
actinolite
actinometer
actinomorphic
actinomycete
actinomycin
actinomycosis
actinopterygian
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actinium
ac·tin·i·um [ ak tínnee əm ]


noun 
Definition:
 
radioactive element: a radioactive silvery white metallic element. Source: pitchblende. Use: source of alpha rays.
Symbol  Ac
[Early 20th century. < Greek aktin- "ray"]
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