| Answer | Crossword Clue |
|---|---|
| HOUR | Fixed point of time. |
| ERA | Fixed point of time. |
| era | a fixed point in time from which a series of years is reckoned |
| ERA | A fixed point in time |
| tautochrone | a curve such that a particle travelling along it under gravity reaches a fixed point in the same time, no matter where it starts |
| tautochrones | TAUTOCHRONE, a curve such that a particle travelling along it under gravity reaches a fixed point in the same time, no matter where it starts |
