Definition of auxin
1
: any of various usually acidic organic substances that promote cell elongation in plant shoots and usually regulate other growth processes (such as root initiation): such as
b
: any of various synthetic substances (such as 2,4-D) resembling indoleacetic acid in activity and used especially in research and agriculture
2
: plant hormone
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Merriam-Webster unabridged
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Time Traveler for auxin
The first known use of auxin was in 1933
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