ADJ.
under
VERB + CHUNTER
continued, let
CHUNTER + NOUN
breath
verb
To speak in a soft, indistinct manner, mutter.
Ron continued to chunter under his breath all the way down the street.
To grumble, complain.
Since she had another seat and was quite comfortable, we smiled and let her chunter.
i Register
In some senses, chunter is marked as British. Watch for register when choosing this word.