The word "curtainraiser" refers to an act or event designed to introduce or preview a performance or event. Some antonyms for this term could include "finale," "closing act," or "climax." These words all suggest an ending or conclusion instead of an opening or preview. Another antonym could be "surprise," as a curtainraiser typically prepares the audience for what is to come, while a surprise might catch them off-guard or be completely unexpected. Other possible antonyms could include "epilogue," "postlude," or "aftermath," which all suggest a conclusion or aftermath rather than an introduction.