- (comparable, rare) Approximating or approaching exact equivalence.
- (not comparable) Bearing full likeness by having precisely the same set of characteristics; indistinguishable.
- (not comparable, mathematics) Exactly equivalent.
- (not comparable, biology) Of twins, sharing the same genetic code.
- (not comparable) Not different or other; not another or others; not different as regards self; selfsame; numerically identical.
- An identical twin.
- (usually pluralized, chiefly philosophy) Something which has exactly the same properties as something else.