| PHOTON | A massless particle which moves at the speed of light in vacuum; it exhibits properties of both waves and particles |
| PRECLUDE | Rule out mention of speed of light in introduction (8) |
| LIGHT | Phenomenon that exhibits characteristics of both waves and particles |
| NOOBJECT | Beginner finding speed of light in plane doable? |
| COLLECTINGDUST | "I sold my old vacuum; it was just __" |
| NOMATTER | Vacuum - it makes no difference |
| OPENING | First performance of a play; a job vacancy; or, a sequence of moves at the start of a game of chess (7) |
| TRANSONIC | No trains running at the speed of light or at the speed of sound (9) |
| SPIN | The intrinsic angular momentum of a subatomic particle which also creates a magnetic moment (4) |
| IGNITE | In its design it exhibits the way it can light up (6) |
| VOLLEYBALL | Sport that involves the moves at the beginning of the *clue answers |
| SIGNAL | Early form of train control, using a metal arm and a spectacle holding coloured lenses which move in front of a lamp (6) |
| SEMAPHORE | Early form of train control, using a metal arm and a spectacle holding coloured lenses which move in front of a lamp (9) |
| CHRISTMASSPIRIT | Enthusiasm for the holiday that falls on December 25: 2 wds. (Theme answer: The circled letters, which move left-to-right across the puzzle, spell a word in the title) |
| RIBOSOME | Particle which is the site of protein synthesis in a cell |
| TRIATOMIC | Water is converting it to air, absorbing mass at the speed of light (9) |
| COSMICRAY | Funny comics in school produced by traveller at the speed of light (6,3) |
| COGNAC | Is able to travel up at the speed of light to get a drink (6) |
| GASSTATIONS | Businesses with pumps for cars and trucks: 2 wds. (Theme answer: The circled letters, which move left-to-right across the puzzle, spell a word in the title) |
| LOCUST | Insect of the family Acrididae, which moves in large migratory swarms and destroys crops and vegetation (6) |
