IPA: /ˈbreɪkˌnɛk/
KK: /ˈbreɪkˌnɛk/
Extremely fast or dangerous, often in a way that could lead to accidents.
The car raced down the road at a breakneck speed, making everyone nervous.
Breakneck → It is formed from "break" (from Old English "brecan", meaning to shatter or destroy) and "neck" (from Old English "hnecca", meaning the part of the body connecting the head to the torso). The word "breakneck" describes a speed that is so fast it could cause one to break their neck, implying extreme danger.
Imagine going so fast that you could 'shatter' ('break') something as vital as your 'neck' — that's why 'breakneck' means dangerously fast.
No commonly confused words.