1. Godan verb with 'u' ending, Intransitive verb

   to laugh

   クラスのもの皆が彼の冗談に笑った。

2. to smile

3. Godan verb with 'u' ending, Transitive verb

   to sneer; to ridicule

   esp. 嗤う

4. Godan verb with 'u' ending, Intransitive verb

   to be dumbfounded; to be flabbergasted

   as 笑ってしまう or 笑っちゃう

Also written 嗤う【わらう】warau