jackknife jackk·nife uncommon noun (2) verb (1) noun 1. a large knife with one or more folding blades Synonymsclasp knife 2. a dive in which the diver bends to touch the ankles before straightening out verb 1. dive into the water bending the body at the waist at a right angle, like a jackknife Related words Word family jackknife-fishjackknife clam Broader terms divepocketknife WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.
