1. A word having the same spelling as another, but a different pronunciation and meaning: Two examples of heteronymy are "lead" guide dog and "lead" as a metal.

Heteronymy is the opposite of homonym and synonym.
2. In ophthalmology, the noncorresponding vertical halves of the visual fields of both eyes: Heteronymy refers to the nasal half of the left eye and the nasal of the right, or the temporal half of the left eye and the temporal of the right.