Definitions of headlong:

• adjective:   excessively quick

  Example: "A headlong rush to sell"

• adjective:   with the head foremost

  Example: "A headlong dive into the pool"

• adverb:   with the head foremost

  Example: "The runner slid headlong into third base"

• adverb:   in a hasty and foolhardy manner

  Example: "He fell headlong in love with his cousin"

• adverb:   at breakneck speed

  Example: "Burst headlong through the gate"