Precursor

Forerunner. That which precedes or is derived from an available source. The term "precursor" is applied to an inactive substance converted to an active one (such as an enzyme, vitamin, or hormone). The term "precursor" applies to any chemical that is transformed into another. From the Latin "praecursor," composed of "prae-" (or pre-), before + "curro" to run = to run before.

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That which precedes another or from which another is derived, applied especially to a physiologically inactive substance that is converted to an active enzyme, vitamin, hormone, etc., or to a chemical substance that is built into a larger structure in the course of synthesizing the latter. [L. praecursor, fr. prae-, pre- + curro, to run]

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pre·cur·sor pri-'kər-sər, 'prē-. n

1) one that precedes and indicates the onset of another <angina may be the \precursor of a second infarction>

2) a substance, cell, or cellular component from which another substance, cell, or cellular component is formed esp. by natural processes

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pre·cur·sor (preґkər-sər) [L. praecursor a forerunner] 1. something that precedes. 2. in biological processes, a substance from which another, usually more active or mature substance is formed. 3. in clinical medicine, a sign or symptom that heralds another.