- a large pocketknife
- 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
Origin of jackknifejack- + knife
transitive verb-·knifed·, -·knif·ing
- to cut with a jackknife
- to cause to jackknife
- to bend at the middle as in a jackknife dive
- to turn on its hitch so as to form a sharp angle: said as of a tractor-trailer after a driving accident
- A large clasp knife.
- Sports A dive in the pike position, in which the diver straightens out to enter the water hands first.
verbjack·knifed, jack·knif·ing, jack·knifes
- To fold or double (something or oneself) like a jackknife.
- To cut or stab with a jackknife.
- To bend or fold up like a jackknife: A truck that had jackknifed was blocking the road.
- To form a 90° angle.
(third-person singular simple present jackknifes, present participle jackknifing, simple past and past participle jackknifed)
- Alternative spelling of jack-knife.