'Breakneck' definitions:

Definition of 'breakneck'

From: WordNet
adjective
Moving at very high speed; "a breakneck pace"

Definition of 'Breakneck'

From: GCIDE
  • Breakneck \Break"neck`\, n.
  • 1. A fall that breaks the neck. [1913 Webster]
  • 2. A steep place endangering the neck. [1913 Webster]

Definition of 'Breakneck'

From: GCIDE
  • Breakneck \Break"neck`\, a. Producing danger of a broken neck; as, breakneck speed. [1913 Webster]