To show clearly and deliberately; manifest: demonstrated her skill as a gymnast; demonstrate affection by hugging. To show to be true by reasoning or adducing evidence; prove: demonstrate a proposition. To present by experiments, examples, or practical application; explain and illustrate: demonstrated the laws of physics with laboratory equipment. To show the use of (an article) to a prospective buyer: The salesperson plugged in and demonstrated the vacuum cleaner. To give a demonstration: described the dance step, then took a partner and demonstrated. To participate in a public display of opinion: demonstrated against tax hikes.