Yahoo Search box for Physics:
"Brownian movement": twenty sites.
"Brownian motion": seventeen sites.
Seems pretty even.


How odd, in that Google seach gives a great discrepency (but with each used enough to suggest that either one is acceptable):
"brownian movement": 8,720 hits.
"brownian motion": 51,300 hits.

AHD says, "Brownian movement ... [definition] ... Also called Brownian motion."