plural jackknives
1
: a small knife that has a folding blade : pocketknife
2
: a dive in which you bend from the waist and touch your ankles and then straighten out
jackknifes; jackknifed; jackknifing
: to bend in the middle like a folding jackknife
especially, of a large truck
: to have the back part slide out of control toward the front part
The truck jackknifed on the icy road.
Cite this Entry
“Jackknife.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/jackknife. Accessed 23 Jun. 2026.
Copy Citation
