means Unable to rest, relax, or stay still — whether in body, mind, or mood.

from A transparent English build: "rest" plus the negating suffix "-less," the same "-less" that gives us "hopeless" and "fearless," from Old English "-leas" meaning "free from, without." "Rest" itself comes from Old English "rest," originally a sense of repose or a resting-place — possibly tied to an old Germanic root for a stretch or stage of a journey, the pause between travels. So "restless" is literally "without that pause" — the journey that won't let you stop.