嘻 (xī) is an interjection used to express sudden emotions such as surprise, alarm, or sorrow—similar to 'Ah!' or 'Oh!' in English. It often appears at the beginning of an utterance, followed by the rest of the sentence. This character also appears in other words (like 笑嘻嘻 'grinning' or 嘻哈 'hip-hop'), but as a standalone interjection it signals a strong reaction to something unexpected or regrettable.