to leave secretly

He slipped away while we were all sleeping. 当我们还在睡觉时他悄悄地离开了。

If a period of time slips away, it passes quickly.

Time was slipping away and she had to make a decision soon. 时间过得很快，她必须很快做出决定。

If someone's power or the possibility of someone winning or achieving something slips away, it disappears.

Political power was really in their hands and they let it slip away. 他们曾一度掌握着很大的政治权力，但却没有把握住。