To be at a loss; to be stumped or nonplussed—unable to respond or know what to say.
上司の理不尽な要求に閉口した。
I was at a loss because of my boss's unreasonable demands.
彼の説明があまりにも専門的で、聞いている側は皆閉口していた。
His explanation was so technical that everyone listening was at a loss.
突然の質問に閉口して、何も答えられなかった。
I was stumped by the sudden question and couldn't answer anything.
To be fed up; to be tired of something; to be unable to bear or annoyed by it.
同じ話を何度も聞かされて閉口した。
I was fed up with hearing the same story over and over.
あの店員の態度には閉口して、もう二度と行かないと決めた。
I was fed up with that clerk's attitude and decided never to go there again.
隣の工事の騒音に閉口している。
I'm fed up with the noise from the construction next door.