actinoid

adjective
ac·​ti·​noid | \ˈak-tə-ˌnȯid \

Definition of actinoid 

(Entry 1 of 2)

1 : resembling a ray especially of a radially symmetrical animal

2 : exhibiting radial symmetry

actinoid

noun
ac·​ti·​noid | \ˈak-tə-ˌnȯid \
plural actinoids

Definition of actinoid (Entry 2 of 2)

chemistry

: actinide The actinoid elements (or actinides; An) constitute a series of 14 elements which are formed by the progressive filling of the 5f electron shell and follow actinium in the periodic table (atomic numbers 90-103).— Mirtat Bouroushian, Electrochemistry of Metal Chalcogenides, 2010

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First Known Use of actinoid

Adjective

1846, in the meaning defined at sense 1

Noun

1958, in the meaning defined above

History and Etymology for actinoid

Adjective

actin(ia) + -oid entry 2 (probably after actinoida or actinoidea )

Noun

actin(ide) + -oid entry 1

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The first known use of actinoid was in 1846

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