1. the speed at which light travels in a vacuum, approximately 186,000 miles per second or 300,000 kilometers per second
Usage: physics; often used in scientific and technical contexts
2. extremely fast speed; rapid movement or action
Usage: informal; figurative

Examples

• Nothing can travel faster than lightspeed according to Einstein's theory of relativity.
• The spacecraft accelerated to near lightspeed as it left the solar system.
• She worked at lightspeed to finish the project before the deadline.
• The internet connection was so fast it felt like lightspeed.
• The company expanded at lightspeed during the tech boom.
• Light travels at lightspeed, which is why we see distant stars almost instantly.