1. A person or thing that comes before another of the same kind and that in some way anticipates or resembles it.
> *The earliest forms of life on Earth were the precursors of all subsequent life.*
2. A substance that is converted into another substance in a chemical reaction.
> *Glucose is a precursor to glycogen.*
3. A forerunner, harbinger, or predecessor.
> *The music was a precursor to the dance.*
4. A herald or omen.
> *The storm was a precursor of disaster.*