Answer:

mutter

Answer	Crossword Clue
MUTTER	Be hard to hear
MUTTER	Grumble
MUTTER	Under-one's-breath sound

MUTTER	Complain in a murmur
MUTTER	Complain under one's breath
MUTTER	Say under one's breath
MUTTER	Speak indistinctly
MUTTER	Murmur indistinctly
MUTTER	Grumble quietly
MUTTER	Grumble.
MUTTER	Speak indistinctly.

MUTTER	Speak low.
MUTTER	Not say clearly
MUTTER	[Grumble, grumble, grumble]
MUTTER	Say inaudibly
MUTTER	Express irritation, maybe

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.