0 to speak quietly and in a way that is not clear so that the words are difficult to understand: --
She mumbled something about being too busy.
[ + speech ] "I'm sorry," he mumbled.
1 to speak quietly or in an unclear way so that the words are difficult to understand: --
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Vi kan slutföra det steg för steg hur lång vägen än är och den kan inte slutföras hur kort vägen än är om du inte ens markerar ditt fotavtryck.