Main Entry: ²jackknife

Function: verb

Date: 1806

transitive verb

1 : to cut with a jackknife
2 : to cause to double up like a jackknifeintransitive verb 1 : to double up like a jackknife <jackknifed into a seat beside me, folding up his six feet eight — Lady Bird Johnson>
2 : to turn and form an angle of 90 degrees or less with each other —used especially of a tractor-trailer combination