1905, from Greek hormon "that which sets in motion," present participle of horman "impel, urge on," from horme "onset, impulse," from PIE *or-sma-, from root *er- "to move, set in motion." Used by Hippocrates to denote a vital principle; modern meaning coined by English physiologist Ernest Henry Starling (1866-1927). Jung used horme (1915) in reference to hypothetical mental energy that drives unconscious activities and instincts. Related: Hormones.