Out cold is a colloquial phrase used to describe someone who has lost consciousness or has become completely unconscious. Synonyms for this term include knocked out, unconscious, senseless, comatose, unresponsive, immobile, inert, lifeless, dead to the world, and in a stupor. These words can be used interchangeably to convey the same meaning, depending on the context. While knocked out and unconscious denote a temporary state of being, comatose and lifeless suggest a more permanent and severe condition. Similarly, out cold, dead to the world, and in a stupor imply a certain degree of lethargy, while unresponsive and immobile suggest a lack of reaction or movement.