identical

Identical is an adjective meaning exactly alike, with no difference in any detail. It is used to describe things that are indistinguishable in appearance, structure, or value, such as two objects produced as copies or two events that share every property.

In biology, the term is common in the phrase identical twins, referring to monozygotic siblings that originate from the same fertilized egg. Identical twins typically share nearly the same genetic material, though small differences can arise from environmental factors and developmental processes.

In mathematics and logic, identical often denotes identity—the relation that two expressions or objects are the very same object. If x is identical to y, then x and y refer to the same entity, not merely to objects that are equal in value or similar in form. The identity relation is reflexive, symmetric, and transitive, and it underpins formal reasoning about equality and substitution.

In everyday usage, identical can describe copies, models, or references that match in every relevant aspect. It is typically stronger than simply being equal in value or function, because it stresses the notion of being the same object or the same instance.

Etymology: identical comes from the Latin identicus, from idem meaning “the same,” and was formed through French and English usage to convey exact sameness.

See also: identity, sameness, identical twins, isomorphism.