jackknife

noun pl. jackknives

1. a large pocketknife
2. a dive in which the diver keeps his knees unbent, touches his feet with his hands, and then straightens out just before plunging into the water

transitive verb jackknifed, jackknifing

1. to cut with a jackknife
2. to cause to jackknife

intransitive verb

1. to bend at the middle as in a jackknife dive
2. to turn on the hitch so as to form a sharp angle with each other: said of a vehicle and its trailer