If you're motionless, you're completely still, not moving a muscle. Your barber might instruct you to remain motionless while he trims the hair around your ears.
Anything that's motionless doesn't move — a statue is motionless, and your bike is motionless lying in the driveway until you climb on it and start pedaling. Photographs are motionless, while video records movement. Your new puppy might be a constantly wiggling, jumping ball of motion until she becomes exhausted and falls sound asleep, motionless. Motion, or movement, comes from a Latin root, motionem, "a movement" or "an emotion."