名詞 mumble:

1. a soft indistinct utterance

動詞 mumble:

1. talk indistinctly; usually in a low voice
   同義詞：mutter, maunder, mussitate
2. grind with the gums; chew without teeth and with great difficulty
   同義詞：gum

1. She mumbled that she didn't want to get up yet.
   她咕噥著說還不想起床。
2. He always mumbles when he's embarrassed.
   他感到難為情時就說話不清楚了。
3. I heard an incoherent mumble.
   我聽到了不連貫的低語聲。

mum.ble

v.（動詞）
mum.bled,mum.bling,mum.bles
v.tr.（及物動詞）
To utter indistinctly by lowering the voice or partially closing the mouth:
咕噥：通過降低聲音或半閉著嘴的方式不清晰地說出：
例句：
mumbled an insincere apology.
含糊地說出無誠意的道歉

To chew slowly or ineffectively without or as if without teeth.
抿著嘴嚼：用沒有或好象沒有牙齒的牙床慢慢地咀嚼
v.intr.（不及物動詞）
To speak words indistinctly, as by lowering the voice or partially closing the mouth.
咕噥：通過降低聲音或半閉著嘴的方式不清晰地講話
To chew food slowly or ineffectively, as if with the gums.
抿著嘴嚼：好象是用牙床慢慢地咀嚼食物
n.（名詞）
A low, indistinct sound or utterance.
含糊的話：低的不清晰的聲音或語調(diào)

來源：
Middle English momelen
中古英語 momelen
from Middle Dutch mommelen
源自 中古荷蘭語 mommelen

【引伸】
mum.bler
n.（名詞）
mum.bly
adj.（形容詞）