| Answer | Crossword Clue |
|---|---|
| envelope | surface tangent to each of a family of surfaces |
| envelopes | A curve or surface tangent to each of a family of curves or surfaces |
| envelope | curve tangent to each of a family of curves |
| riffler | A narrow elongated tool with a curved file surface at each end, used in filing concave surfaces |
| trajectories | A curve or surface cutting a family of curves or surfaces at a constant angle |
| trajectory | A curve or surface cutting a family of curves or surfaces at a constant angle |
