"notice beforehand of the consequences that will probably follow continuance in some particular course" [Century Dictionary], Old English warnung, verbal noun from warnian (see warn (v.)).
权威例句
1. Without warning, Bardo smacked his fist into his open hand.
巴多没有任何预兆地一拳砸在自己摊开的手掌上.
2. The driver managed to escape from the vehicle and shout a warning.
那名司机设法从车里逃了出来并大声警告别人。
3. I had this uncanny feeling that Alice was warning me.
我有一种奇怪的感觉:艾丽斯是在警告我。
4. Then without warning, the troops opened fire on the crowd.
接着军队未作警示便向人群开了火。
5. Mr Straw issued a stern warning to those who persist in violence.