instantaneous

Everyday

1. Happening immediately, with no delay at all. tree →
2. (science) At one exact instant of time: instantaneous speed. tree →

In the lessons

In science, light from a nearby lamp seems to arrive instantaneously (it's very fast but not truly instant); in maths and physics, instantaneous speed is the speed at a single moment, like a speedometer reading, compared with average speed over a journey. In everyday life, messages and reactions can be instantaneous. Phrases: instantaneous reaction, almost instantaneous, instantaneous speed.

Examples

• The reaction was instantaneous: the mixture fizzed straight away. tree →
• Text messages arrive almost instantaneously. tree →
• The speedometer shows your instantaneous speed. tree →
• When you flick the switch, the light seems instantaneous. tree →
• Her answer was instantaneous; she didn't need to think. tree →
• Death of the cells was instantaneous in the boiling water. tree →
• It was impossible to tell, the shock was so instantaneous. tree →

Note

Spelling: in-stan-ta-ne-ous. Similar: «instant», «immediate». In science, average speed = distance ÷ time; instantaneous speed is the speed at one moment, which can be different.