It's a Particle of Light
This page is the CodyCross answer for the clue below from The 70's, Group 331, Puzzle 3 (The Concorde).
Question is: It's a Particle of Light
and the answer is: PHOTON
Word Meaning:
PHOTON — (particle physics) The quantum of light and other electromagnetic energy, regarded as a discrete particle having zero rest mass, no electric charge, and an indefinitely long lifetime. It is a gauge boson.
Definitions from Wiktionary.