Alphabetically, It's the First Chemical Element

This page is the CodyCross answer for the clue below from Games, Group 945, Puzzle 5 (Infinite Health).

Question is: Alphabetically, It's the First Chemical Element

and the answer is: ACTINIUM

Word Meaning:

ACTINIUM — A radioactive, metallic chemical element (symbol: Ac) with an atomic number of 89; found in uranium ores.

Definitions from Wiktionary.