To disparage or speak ill of someone/something; to belittle or denigrate.
人の努力をけなすのはやめたほうがいい。
You should stop belittling people's efforts.
彼は会議で同僚の提案を平然とけなした。
He calmly disparaged a colleague's proposal during the meeting.
匿名の書き込みで自分の作品をけなされて傷ついた。
I was hurt when my work was disparaged in anonymous posts.