1. A large clasp knife.
2. sports A dive in the pike position, in which the diver straightens out to enter the water hands first.
3. to fold or double (something or oneself) like a jackknife.
4. to cut or stab with a jackknife.
5. to bend or fold up like a jackknife: A truck that had jackknifed was blocking the road.
6. to form a 90° angle.

1. alternative spelling of jack-knife.
2. A resampling method that applies estimators to all subsamples that each omit a single different group (possibly of a single datapoint) of the original sample to provide a sample distribution of the estimate.
3. alternative spelling of jack-knife.

1. A large, strong clasp knife for the pocket; a pocket knife.

1. A pocket-knife larger than a penknife.
2. A horn-handled clasp-knife with a laniard, worn by seamen.
3. A form of terminal used for making connections in central telephone-stations. see jack, 11 .

1. dive into the water bending the body at the waist at a right angle, like a jackknife
2. a large knife with one or more folding blades
3. a dive in which the diver bends to touch the ankles before straightening out