形容詞 headfirst:

1. with the head foremost
   同義詞：headlong

副詞 headfirst:

1. with the head foremost
   同義詞：headlong

1. 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.
   屈體跳水，鐮刀式跳水頭向下的一種跳水動(dòng)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(shì)跳入水中以前，要先用手觸腳

head.first

adv.（副詞）
With the head leading; headlong:
頭部在先地；頭朝前地：
例句：
went headfirst down the stairs.
一頭栽下了樓梯

Impetuously; brashly.
魯莽地；輕率地

【引伸】
head.first.
adj.（形容詞）