jackknife

n. 大折合式刀, 屈体跳水
vi. 弯身
vt. 用大 * 切

动词过去式:jackknifed 过去分词:jackknifed 现在分词:jackknifing 第三人称单数:jackknifes 

jack.knife

n.（名词）
A large clasp knife.
大折刀
Sports A dive executed by jumping headfirst, bending the body at the waist, and, with the legs straight, touching the feet with the hands before straightening out to enter the water hands first.
【体育运动】 屈体跳水，镰刀式跳水：头向下的一种跳水动作，把身体弯到腰部、腿伸直，在打开身体且以手先触水的姿势跳入水中以前，要先用手触脚
v.（动词）
jack.knifed,jack.knif.ing,jack.knifes
v.tr.（及物动词）
To fold or double (something or oneself) like a jackknife.
折叠：折刀似的折拢或折叠（某物或其自身）
To cut or stab with a jackknife.
用折刀切或刺
v.intr.（不及物动词）
To bend or fold up like a jackknife:
折起来：折刀似的折弯或折叠：
例句：
A truck that had jackknifed was blocking the road.
那辆被撞弯的卡车正堵塞着道路

To form a 90= angle.
形成九十度角