Not moving; completely still or stationary without any action or movement.
From 'motion' (from Latin 'motio', movement) plus the suffix '-less' (without). The term became common in the 1600s to describe absolute stillness.
In physics, 'motionless' is actually impossible—according to Einstein's relativity, everything is always in motion relative to something else, so even what appears motionless is technically moving through space and time.
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