jackknife       
 verb [ I ] uk/ˈdʒæk.naɪf/ us/ˈdʒæk.naɪf/
 弯成V字形(如铰接货车的弯折)
If a truck that has two parts jackknifes, one part moves around so far towards the other part that it cannot be driven.
  The oil tanker jackknifed after skidding on the ice. 油罐车在冰上打滑,绞接的车身之间发生了弯折。 
 jackknife       
noun [ C ] uk/ˈdʒæk.naɪf/ us/ˈdʒæk.naɪf/  jackknives
 大折刀
a large knife with a blade that folds into the handle
 Synonym: clasp knife