1.show or demonstrate something to an interested audience;
She shows her dogs frequently
2.establish the validity of something, as by an example, explanation or experiment;
The experiment demonstrated the instability of the compound
3.provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes;
His high fever attested to his illness
4.march in protest; take part in a demonstration;
Thousands demonstrated against globalization during the meeting of the most powerful economic nations in Seattle