adj. 25B6; adjective the breakneck pace of change : EXTREMELY FAST, rapid, speedy, high-speed, lightning, whirlwind.
25A0; at breakneck speed DANGEROUSLY FAST, at full tilt, flat out, ventre à terre; informal hell for leather, like the wind, like a bat out of hell, like greased lightning; Brit. informal like the clappers.