n :  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 : also  :  a reflex reaction involving a tropism tro*pis*tic adj 
 
 
 
Similar sounding terms:  tra·pe·zi·um 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2008.