breakneck (adj.)
- abrupt
- accident-prone
- agile
- bluff
- bold
- breathless
- careless
- dangerous
- daredevil
- dashing
- desperate
- devil-may-care
- double-quick
- excessive
- expeditious
- express
- fast
- fleet
- flying
- furious
- harum-scarum
- hasty
- headlong
- hotheaded
- hurried
- impetuous
- impulsive
- light-footed
- lively
- mad
- mercurial
- nimble
- overeager
- overenthusiastic
- overzealous
- precipitant
- precipitate
- precipitous
- prompt
- quick
- rapid
- rash
- reckless
- running
- sharp
- sheer
- slapdash
- snappy
- spanking
- speedy
- steep
- sudden
- swift
- vertical
- wanton
- wild
- winged
