Ichthys

Ichthys, also transliterated ichthus, is the Greek word for fish. The term forms the basis of many scientific words in ichthyology—such as ichthyofauna and ichthyosaur—where the root ichth- or ichthy- denotes fish and related ideas.

In Christian tradition, the ichthys symbol—a simple outline of a fish formed by two intersecting arcs—was used as a discreet sign of faith in times of persecution. It is often described as an acronym: Iēsous Christos Theou Huios Sōtēr, or “Jesus Christ, Son of God, Savior,” though its historical origin as a coded message is debated. The symbol appeared in early Christian art, tombs, and inscriptions, and continues to appear in modern jewelry, logos, and church ornamentation.

Today the word and symbol have broad recognition beyond religious contexts. The Greek root ichth- remains common in biology and taxonomy, yielding terms such as ichthyology (the study of fish), ichthyofauna (the animal life of a region’s fishes), and related names for fossil and living fish and fish-like organisms. The term is part of the broader linguistic legacy of ancient Greek in science and culture.