/ ˈtrəʊpɪzəm; ˈtrɒp-; NAmE ˈtroʊpɪzəm/ noun
[ U ] ( biology ) the action of a living thing turning all or part of itself in a particular direction, towards or away from sth such as a source of light
••
WORD ORIGIN
late 19th cent.: from Greek tropos turning (from trepein to turn) + -ism .