As verbs the difference between muttering and grumbling
is that muttering is present participle of lang=en while grumbling is present participle of lang=en.
As nouns the difference between muttering and grumbling
is that muttering is something which is muttered while grumbling is complaining.
muttering
English
Verb
(head)
Noun
(
en noun)
Something which is muttered
- I managed to catch a few of his mutterings .
A rumour.
Synonyms
* (something muttered) mumblage