| Answer | Crossword Clue |
|---|---|
| contrapropeller | one of a pair of propellers rotating in opposite directions |
| couple | A pair of equal and parallel forces acting in opposite directions, and tending to cause rotation about an axis perpendicular to the plane containing them |
| couples | A pair of equal and parallel forces acting in opposite directions, and tending to cause rotation about an axis perpendicular to the plane containing them |
