“Dead ringer” means that someone or something that looks exactly like another person or thing. It’s used to emphasize striking resemblance. The phrase combines “ringer” — originally a fraudulently substituted competitor, especially a horse entered into a race in place of a faster animal — with “dead,” an intensifier meaning “exact” or “complete.”

By the late 1800s “ringer” referred to a look‑alike as well as a substitute; “dead ringer” appears in print from around 1891 to stress near‑perfect likeness.

In everyday use, “dead ringer” is informal and conversational. It often describes physical similarity, but can also apply to mannerisms or vocal likeness. Synonyms include “spitting image,” “carbon copy,” and “double,” although each carries slightly different tones. “Spitting image” is equally emphatic and informal, while “carbon copy” suits written language.