Answer:

breakneck

Answer	Crossword Clue
BREAKNECK	Reckless, as speed
BREAKNECK	Overfast
BREAKNECK	Suicidally reckless.

BREAKNECK	Recklessly fast
BREAKNECK	Too fast

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.