from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A large clasp knife.
  • noun Sports A dive in the pike position, in which the diver straightens out to enter the water hands first.
  • intransitive verb To fold or double (something or oneself) like a jackknife.
  • intransitive verb To cut or stab with a jackknife.
  • intransitive verb To bend or fold up like a jackknife.
  • intransitive verb To form a 90° angle.

from The Century Dictionary.

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

from the GNU version of the Collaborative International Dictionary of English.

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

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun Alternative spelling of jack-knife.
  • noun statistics 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.
  • verb Alternative spelling of jack-knife.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

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


Sorry, no etymologies found.


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  • As a statistical term:

    Jackknifing, which is similar to bootstrapping, is used in statistical inferencing to estimate the bias and standard error in a statistic, when a random sample of observations is used to calculate it. The basic idea behind the jackknife estimator lies in systematically recomputing the statistic estimate leaving out one observation at a time from the sample set. From this new set of "observations" for the statistic an estimate for the bias can be calculated and an estimate for the variance of the statistic.

    (Source: Wikipedia)

    November 25, 2009

  • This brings back hideous memories of a night, back in the dark ages of 1988, spent in the lovely Radisson hotel in downtown Muncie, Indiana, where I discovered an egregious computational error in the presentation I was due to give at the next day's conference, and so ended up having to jackknife the key numerical result - with only a pocket calculator - by hand in my hotel room. As there were 72 observations in the dataset, this involved 72 recalculations of the statistic in question. As I recall, it took me until 4 in the morning, and involved three brandies from the minibar, as well as a club sandwich and french fries delivered from room service at around 2am. The audience was none the wiser, except perhaps for the telltale residue of french fry grease that besmirched a few of the transparencies.

    I learned a valuable lesson about the inadvisability of jackknifing without the appropriate technological tools.

    November 25, 2009

  • You should not have been diving with all that food in your belly, 'nach. Also, I'm thinking the pools at the Radisson probably are not even deep enough to dive safely.

    November 25, 2009

  • "I'm thinking the pools at the Radisson probably are not even deep enough to dive safely. "

    Something tells me that you've never been in beautiful downtown Muncie, dc. All-you-can-eat buffet? Yes! "Swimming pool"? Not a priority in the midwest. :-)

    November 25, 2009

  • dontcry: HA!

    November 25, 2009

  • This is all I know about Indiana: Gary, Indiana, Gary, Indiana, Gary, Indiana...

    November 25, 2009

  • The person or the place?

    November 25, 2009

  • The song.

    November 25, 2009

  • So we have unmasked sionnach as the infamous Jack the Knife?

    November 25, 2009