means The dark shape cast on a surface when an object blocks a source of light, or more loosely any patch of relative darkness, dimness, or a faint imitation of something.

from From Old English 'sceadu,' meaning shade, shadow, or darkness — the same root that also gives us 'shade,' the two words splitting like a forked path from one Germanic ancestor (compare Old High German 'scato'). It reaches back to a Proto-Germanic root meaning shade or screen, and scholars trace it further to a Proto-Indo-European root '*skot-' meaning dark or shade, a possible cousin of the Greek 'skotos,' darkness. So the word has always lived in the dim places, long before anyone measured how fast they travel.