mumbler

Từ điển WordNet v3.1 - WordNet Dictionary

noun

a person who speaks softly and indistinctly
• Syn:
mutterer, murmurer
• Derivationally related forms:
murmur (for: murmurer), mumble, mutter (for: mutterer)
• Hypernyms:
speaker, talker, utterer, verbalizer, verbaliser