as fast as the speed of light

1. adjective Incredibly quick or speedy. Did you see that martial arts expert? Those kicks were as fast as the speed of light! The microprocessor at the heart of the supercomputer is as fast as the speed of light. If you're in a rush, use this printer—it's as fast as the speed of light.

2. adverb Incredibly quickly or speedily; as fast as possible. Mary raced out of the room as fast as the speed of light when she heard the teacher coming. You'd better get to the store early if you want to find a good deal. Everything usually sells out as fast as the speed of light. Wow, that sports car just zoomed by as fast as the speed of light!