grumbling
n. 咕哝；（集体的）隐隐的不满；隆隆声
adj. 出怨言的，喃喃鸣不平的
v. 发牢骚；发轰隆声；（内脏）间歇性地闹病（grumble 的现在分词）
例句
Although he was only grumbling, his choice of words made Rodney angry.
尽管他只是在发牢骚，但他所用的字眼却让罗德尼很生气。
《柯林斯英汉双解大词典》
Nothing pleased him. He was always grumbling.
没有什么能使他满意，他总是发牢骚。
《新英汉大辞典》
They kept grumbling that they were cold.
他们不停地嘟囔着说冷。
《牛津词典》
