onset /ˈɔnset]/ n. [u] 1. 开始：at the onset of the war战争开始时The drug must be taken from the onset of the infection.这种药必须在感染的最初期就开始服用。2. 攻击：the sudden onset of the disease疾病的突然发作Our troops withstood the onset of the enemy.我们的部队抵挡住了敌人的进攻。