Precursor in Microsoft Dictionary

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precursor

pre·cur·sor [prə kúrssər, pr kùrssər]
(plural pre·cur·sors)
noun
1.  somebody or something that comes earlier: somebody or something that comes before, and is often considered to lead to the development of, another person or thing
2.  previous holder of job: somebody who held a position or job before somebody else
3.  chemistry chemical compound preceding another: a chemical compound that leads to another, usually more stable, product in a series of connected reactions

[Early 16th century. < Latin praecursor < praecurs-, stem of praecurrere "run before" < currere "run"]

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