"Dead to the world" is an idiom used to describe someone who is completely asleep or unconscious. There are several synonyms that can be used to replace this phrase, depending on the context. These synonyms include "out cold," "sound asleep," "fast asleep," and "deeply unconscious." Other options may include "in a deep sleep," "unresponsive to external stimuli," or even "in a coma." Each of these synonyms can be used to convey the sense of being completely unaware of one's surroundings and completely disconnected from the world. Whether used in casual conversation or in more formal writing, these synonyms allow speakers and writers to express themselves with precision and clarity.