1 (formal 正式) to happen, especially in a way that has not been planned 发生（尤指偶然地）: The accident occurred late last night. 那宗意外于昨天深夜发生。 ☞Look at the note at happen. 参看happen的注释。

2 to exist or be found somewhere 存在；找得到: The virus occurs more frequently in children. 这种病毒更经常存在于儿童身上。

3 occur to sb (used about an idea or a thought) to come into your mind （指主意、想法）（指某人）想起，想到: It never occurred to John that his wife might be unhappy. 约翰从没有想到他的妻子可能会不快活。