Borbottare vs. mormorare
The Italian words borbottare and mormorare both relate to speaking softly or unclearly, but they have distinct nuances in their usage and connotations.
Borbottare
B1Borbottare typically implies complaining or expressing dissatisfaction in a low, grumbling voice. It often suggests a negative or irritated tone.
Il nonno borbottava contro i prezzi alti al supermercato.
(The grandfather grumbled about the high prices at the supermarket.)
Smettila di borbottare e dimmi chiaramente cosa c'è che non va.
(Stop muttering and tell me clearly what's wrong.)
Mormorare
B1Mormorare generally means to speak in a soft, low voice, often implying secrecy or discretion. It can also refer to a gentle, continuous sound like a stream or wind.
I due amici mormoravano tra loro per non farsi sentire dagli altri.
(The two friends murmured to each other to avoid being heard by others.)
Si sentiva mormorare il ruscello in lontananza.
(The stream could be heard murmuring in the distance.)
Summary
While both borbottare and mormorare involve speaking softly, borbottare is more associated with complaining or grumbling, often with a negative tone. Mormorare, on the other hand, is more neutral and can imply secrecy or discretion, or even describe gentle, continuous sounds in nature.