"He kept a jack-knife in his pocket for various tasks."
2.nounThe front-dive pike, in which the body folds and unfolds.
"It took me hundreds of dives to master even the simple jackknife"
3.nounA semi-trailer truck accident in which the vehicle mimics the closing of a jack-knife.
"I have seen several jack-knives along that dangerous stretch of road."
4.nounA 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.