breakneck

break +‎ neck

breakneck (comparative more breakneck, superlative most breakneck)

1. Dangerously fast; hell-for-leather.

   He came running around the corner at a breakneck pace and couldn't stop in time to avoid hitting the fruit stand.

   • 1961 November, H. G. Ellison and P. G. Barlow, “Journey through France: Part One”, in Trains Illustrated, page 668:

     The line to Dunières conists of a series of breakneck descents almost invariably ended by a violent curve and followed immediately by a panting climb, on which the engine barked thunderously but failed unhappily to maintain its booked speed of 13 m.p.h.

breakneck (plural breaknecks)

1. A fall that breaks the neck.
2. A dangerous steep place from which one could fall badly.

• creekbank