1once; one time
2(following a verb) for a moment; briefly
3for a little while; in no time; almost immediately
4all at once; all of a sudden
Examples
yí xià zi一下子zhī jiān之间wǒ我wàng忘le了tā她de的míng zi名字le了。
一下子之间我忘了她的名字了。
For a moment I forgot what her name was.
这个说法一下子就流行开来了。
This saying suddenly became popular.
她一下子就认出他了。
She recognized him immediately.