n. a daily written record of (usually personal) experiences and observations
n. a personal journal (as a physical object)
n. 日记
[经] 日记簿
1. I write in my diary every night before I go to bed.
我每天晚上睡觉前都会写日记。
2. She keeps her diary locked so that no one can read it.
她把日记锁起来，这样没有人能看。
3. My diary helps me remember important events in my life.
我的日记帮助我记住生活中的重要事件。