Valve's First Game Was This First-Person Shooter
This page is the CodyCross answer for the clue below from Cats, Group 1728, Puzzle 1 (Hunting Instincts).
Question is: Valve's First Game Was This First-Person Shooter
and the answer is: HALF-LIFE
Word Meaning:
HALF-LIFE — (nuclear physics) The time required for half the nuclei in a sample of an isotope to undergo radioactive decay.
Definitions from Wiktionary.