PHOTON

Quantum of electromagnetic radiation (6)

Solution has appeared in 2 crosswords (1 across and 1 down):

• Quick crossword No 16,518 — 2023-04-14 23:00:25
  15A: Tiny particle light or electromagnetic radiation (6)
• Quick crossword No 15,500 — 2020-01-11 00:00:51
  14D: Quantum of electromagnetic radiation (6)