Defined: a : one that precedes and indicates the approach of another b : predecessor
2 : a substance, cell, or cellular component from which another substance, cell, or cellular component is formed NOUN (Merriam-Webster.com)
In my neck of the woods this evening, lightning was a precursor to thunder. We finally got a good rain storm!
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1. One that precedes and indicates, suggests, or announces someone or something to come: Colonial opposition to unfair taxation by the British was a precursor of the Revolution.
2. One that precedes another; a forerunner or predecessor: The new principal’s precursor was an eminent educator.
3. A biochemical substance, such as an intermediate compound in a chain of enzymatic reactions, from which a more stable or definitive product is formed: a precursor of insulin.
[Middle English precursoure, from Old French precurseur, from Latin praecursor, from praecursus, past participle of praecurrere, to run before : prae-, pre- + currere, to run; see kers- in Indo-European roots.]
(The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.)