jackknife has definitions from the field of sport
1
[ noun ] a large knife with one or more folding blades

Synonyms

clasp_knife

Related terms

pocketknife

2
[ verb ] dive into the water bending the body at the waist at a right angle, like a jackknife

Related terms

dive sport

3
[ noun ] (sport) a dive in which the diver bends to touch the ankles before straightening out

Related terms

dive

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