the moment at which something begins, and especially something uncomfortable or unpleasant

the onset of winter 冬季的开始

The new treatment can delay the onset of the disease by several years. 新的治疗方法可以把疾病开始的时间延后几年。

The disease must be treated before the onset of symptoms.

The loss in bone tissue increases after the onset of the menopause.

Various signs may indicate the onset of dementia.

It often occurs with the onset of adolescence.