Precursor

n.

1.

One who, or that which, precedes an event, and indicates its approach; a forerunner; a harbinger. Evil thoughts are the invisible, airy precursors of all the storms and tempests of the soul. - Buckminster.

Noun	1.	precursor - a substance from which another substance is formed (especially by a metabolic reaction)
	2.	precursor - a person who goes before or announces the coming of another Synonyms: forerunner
	3.	precursor - an indication of the approach of something or someone Synonyms: harbinger, herald, forerunner

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