motionless
Completely still, without any movement at all.
Motionless means completely still, without any movement at all. When a rabbit freezes in fear, hoping a fox won't notice it, the rabbit becomes motionless: not a whisker twitches, not an ear flickers. A motionless lake on a windless morning looks like glass, its surface perfectly smooth without a single ripple.
You might stand motionless during a game of freeze tag, or watch a lizard sit motionless on a rock as it soaks up the sun's warmth.
Being motionless takes surprising effort. Try sitting completely motionless for just one minute: you'll notice how much you naturally fidget, shift your weight, or blink. Animals like herons use this ability brilliantly, standing motionless in shallow water for minutes at a time, waiting to spear fish with lightning-quick strikes.
Scientists use the word precisely: a motionless object has zero velocity, meaning it's not moving at all relative to whatever you're measuring from.