Answer: muttered

AnswerCrossword Clue
MUTTEREDComplained under one's breath
MUTTEREDSounded unhappy
MUTTEREDTalked indistinctly.
MUTTEREDGrumbled.
MUTTEREDGrumbled indistinctly
MUTTEREDGrumbled
mutteredSay something in a low or barely audible voice, esp. in dissatisfaction or irritation
mutteredMUTTER, to murmur (to make a subdued muttered sound)
mutteredSpeak privately or unofficially about someone or something; spread rumors