[tro.pism] n [ISV -tropism] (1899) 1 a: involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation b: a reflex reaction involving a tropism
2: an innate tendency to react in a definite manner to stimuli; broadly: a natural inclination: propensity -- tro.pis.tic adj