The distance between two consecutive peaks or troughs in a wave, or the distance light or sound travels in one complete cycle.
Compound word from 'wave' (from Old English 'wægn' meaning to move back and forth) and 'length' (from Proto-Germanic, meaning physical extent).
Different wavelengths of light create all the colors you see—red light has longer wavelengths and blue has shorter ones, which is why the sky looks different colors at sunset!
Complete word intelligence in one call. Free tier — 50 lookups/day.