名詞 onset:

1. the beginning or early stages
   同義詞：oncoming
2. (military) an offensive against an enemy (using weapons)
   同義詞：attack, onslaught, onrush

1. A rare congenital disorder of childhood that is characterized by rapid onset of the physical changes typical of old age, usually resulting in death before the age of20.
   (兒童的)早衰癥一種少見的少年身體機能失調(diào)，以類似年老的身體快速變化為特征，其結(jié)果通常導致二十歲之前死亡
2. The attainment or onset of puberty.
   到達青春期或青春期開始
3. He met many difficulties at the first onset.
   在一開始時，他遇到了許多困難。

on.set

n.（名詞）
An onslaught; an assault.
攻擊：襲擊
A beginning; a start:
開始：
例句：
the onset of a cold.
感冒初起