International Scientific Vocabulary, from Greek auxein to increase — more at eke
First Known Use: 1933
Medical Definition of AUXIN
: an organic substance that is able in low concentrations to promote elongation of plant shoots and usually to control other specific growth effects; broadly:plant hormone
Any of a group of hormones that regulate plant growth, particularly by stimulating cell elongation in stems and inhibiting it in roots. Auxins influence the growth of stems toward light (phototropism) and against the force of gravity (geotropism). Auxins also play a role in cell division and differentiation, fruit development, the formation of roots from cuttings, the inhibition of lateral branching, and leaf fall. The most important naturally occurring auxin is beta-indolylacetic acid.