jackknife

詳細解釋：

jack.knife

n.（名詞）
A large clasp knife.
大 *
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.
【體育運動】 屈體跳水，鐮刀式跳水：頭向下的一種跳水動作，把身體彎到腰部、腿伸直，在打開身體且以手先觸水的姿勢跳入水中以前，要先用手觸腳
v.（動詞）
jack.knifed,jack.knif.ing,jack.knifes
v.tr.（及物動詞）
To fold or double (something or oneself) like a jackknife.
摺疊： * 似的折攏或摺疊（某物或其自身）
To cut or stab with a jackknife.
用 * 切或刺
v.intr.（不及物動詞）
To bend or fold up like a jackknife:
折起來： * 似的折彎或摺疊：
例句：
A truck that had jackknifed was blocking the road.
那輛被撞彎的卡車正堵塞著道路

To form a 90= angle.
形成九十度角