n. A class of plant growth substance (often called phytohormones or plant hormones) which play an essential role in coordination of many growth and behavioral processes in the plant life cycle.
the GNU version of the Collaborative International Dictionary of English
n. a substance which, in small concentrations, promotes root formation, bud growth, or certain other processes such as fruit ripening or leaf drop in plants.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a plant hormone that promotes root formation and bud growth
Word Usage
"Arabidopsis thaliana that are defective in the formation of continuous vascular network: calling the auxin signal flow canalization hypothesis into question."