Say the same thing. Or the exact opposite.
A synonym is a word with a similar meaning, like peaceful for calm. An antonym, or opposite, is a word with the opposite meaning, like agitated for calm.
new · good · first · want · even · need · right · work · day · world · life · best · use · look · state · part · find · help · old · own · place · school · end · show · sure · family · please · second · number · lot · real · company · let · different · group · system · care · person · live · change