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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.Medical dictionary. 2011.