形容詞 headlong:

1. excessively quick
   同義詞：hasty
2. with the head foremost
   同義詞：headfirst

副詞 headlong:

1. with the head foremost
   同義詞：headfirst
2. at breakneck speed
   同義詞：precipitately
3. in a hasty and foolhardy manner
   同義詞：rashly

1. A headlong dive or fall.
   頭朝下跳水或掉落
2. The child leaned towards his mother and fell headlong in front of her.
   孩子俯身湊向媽媽，頭朝前面倒在媽媽的面前。
3. Little Marry carried on for ten minutes after she fell headlong.
   小瑪麗摔了個(gè)倒栽蔥后，哭鬧了十分鐘。
4. Don't rush headlong into danger; think it through carefully before you make any decisions.
   不要輕率地奔赴險(xiǎn)境，做任何決定之前都要認(rèn)真想想。

head.long

adv.（副詞）
With the head leading; headfirst:
頭部先著地地；頭沖前地：
例句：
The runner slid headlong into third base.
跑壘者一頭滑進(jìn)了三壘

In an impetuous manner; rashly.
魯莽地；輕率地：用魯莽的方式地；輕率地
At breakneck speed or with uncontrolled force.
飛快地：以極快的速度或無(wú)法控制的力量地
adj.（形容詞）

Done with the head leading; headfirst:
頭在前完成的；頭沖前的：
例句：
a headlong dive.
俯沖跳水

Impetuous; rash.See Synonyms at impetuous
莽撞的；輕率的參見 impetuous
Uncontrollably forceful or fast.
無(wú)法控制的力量或速度的
Archaic Steep; sheer.
【古語(yǔ)】 陡峭的；垂直的

來(lái)源：
From Middle English (bi) hedlong
源自 中古英語(yǔ) (bi) hedlong
from hed, head [head] * see head
源自 hed, head [頭部] *參見 head