Brownian /ˈbɹaʊni.ən/adjective 3forms 2phrases 1 adjective3 •Of or relating to botanist Robert Brown (1773-1858), who investigated the movement of pollen suspended in water. •Pertaining to motion caused by the random vibration of molecules (Brownian motion). •Of or relating to Capability Brown (Lancelot Brown, 1716?–1783), English landscape architect. formsmore Brownian · most Brownian Phrases with Brownian Brownian motionRandom motion of particles suspended in a fluid, arising from those particles being struck by individual molecules of the fluid.