(1):

(a. & adv.) With the head foremost; as, to fall headlong.

(2):

(a. & adv.) Hastily; without delay or respite.

(3):

(a. & adv.) Rashly; precipitately; without deliberation.

(4):

(a.) Rash; precipitate; as, headlong folly.

(5):

(a.) Steep; precipitous.