Definitions for "Actinides"
Elements with atomic numbers from 89 (actinium) or 90 (thorium) to 103 (lawrencium) inclusive.
the row of elements below the periodic table, from thorium to lawrencium.
naturally occurring and/or artificial radioelements with an atomic number (i.e. the number of protons in the nucleus) between 89 (actinium) and 103 (lawrencium)