Noun, Adverb (fukushi), Adverb taking the 'to' particle
grunt; grumble; complaint; mutter
Onomatopoeic or mimetic word
祖父はいつも何やかやぶつぶつ不平を言っていた。My grandfather was always grumbling about something or other. pimples; spots; eruption; rash
cutting into small pieces
simmering
Also written ブツブツ