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to laugh mockingly; to smile with contempt; to jeer; to sneer
Note: usually written せせら笑う
「嘲笑う」 has another reading with different meanings.
人の失敗を嘲笑うのは良くないことだ。
It is not good to sneer at others' failures.
彼女は私の提案を馬鹿にして嘲笑った。
She sneered at my proposal.
嘲笑う人こそ自分を見直すべきだ。
Those who sneer should reflect on themselves.