Noun

1. A relation of direct opposition
2. The gears by which the motion of a machine can be reversed
3. An unfortunate happening that hinders or impedes; something that is thwarting or frustrating
4. The side of a coin or medal that does not bear the principal design
5. (american football) a running play in which a back running in one direction hands the ball to a back running in the opposite direction
6. Turning in the opposite direction

Adjective

1. Of the transmission gear causing backward movement in a motor vehicle

Verb

1. Change to the contrary
2. Turn inside out or upside down
3. Rule against
4. Cancel officially
5. Reverse the position, order, relation, or condition of