vi.

1. 抱怨，发牢骚[（+at/about/over）]
   But there is no use in grumbling.

   可抱怨有什么用呢。

2. 咕哝；发哼声；发轰隆声

vt.

1. 埋怨；对……表示不满[（+out）]
   He grumbled out his reasons for refusing the command.

   他生气地说出拒绝执行该项命令的理由。

n.

1. 怨言，牢骚[C]
   She is full of grumbles.

   她牢骚满腹。

2. 轰隆声[the S]

v.

1. complain in a bad-tempered way.
2. make a low rumbling sound.
3. [usu. as adj. grumbling] (of an internal organ) give intermittent discomfort.

n.

1. a complaint.
2. a grumbling sound.