1. To add alcohol or drugs to food or to drinks: "Someone spiked some of the glasses of fruit juice at the party with vodka."
2. To add something which gives interest or flavor to something: "The student spiked her assigned class report with sarcastic remarks."
3. To increase significantly in a short time: "After going down slightly, the gas prices spiked again."
4. To hit something down sharply towards the ground: "The winning point came in the final seconds when the volleyball player spiked the ball."
5. To form something into points: "It was unusual to see the fitness trainer spiking his hair."