Origin: 1325–75; Middle English demonstracioun < Latin dēmonstrātiōn- (stem of dēmonstrātiō, equivalent to dēmonstrāt(us) (see demonstrate) + -iōn--ion
late 14c., from L. demonstrationem, from demonstrare, from de- "entirely" + monstrare "to point out, show," from monstrum "divine omen, wonder." Meaning "public show of feeling," usually with a mass meeting and a procession, is from 1839.