precursor: Meaning and Definition of

pre•cur•sor

1. a person or thing that precedes, as in a job, a method, etc.; predecessor.
2. a person, animal, or thing that goes before and indicates the approach of someone or something else; harbinger: The first robin is a precursor of spring.
3. a chemical that is transformed into another compound, as in the course of a chemical reaction, and therefore precedes that compound in the synthetic pathway: Cholesterol is a precursor of testosterone.
4. a cell or tissue that gives rise to a variant, specialized, or more mature form.