Actinide

//ˈæktɪnaɪd// noun

noun ·Uncommon ·Advanced level

Definitions

Noun
  1. 1
    Any of the 15 radioactive elements of the periodic table from actinium to lawrencium that are positioned under the lanthanides, to which they have similar chemistry.
  2. 2
    any of a series of radioactive elements with atomic numbers 89 through 103 wordnet
  3. 3
    Any of the 14 elements from actinium to nobelium (lawrencium is excluded by some authors as it is a d-block rather than an f-block element).
  4. 4
    Any of the 14 elements from thorium to lawrencium (actinium having been mistakenly excluded because it was thought to be a d-block element in the past). dated

Synonyms

All synonyms
actinoidactinoidactinonmain group

Example

More examples

"Einsteinium is the name for the element with atomic number 99 and is represented by the symbol Es. It is a member of the actinide group."

Etymology

From actin- + -ide.

Related phrases

periodic table

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.