To speak softly or indistinctly, often in discontent or annoyance.

To express something in a low voice or to mumble, often indicating frustration or impatience.

फुसफुसाना

English Usage: He muttered a few words of frustration when he missed the bus.

Hindi Usage: जब वह बस चूक गया, तो उसने निराशा में कुछ फुसफुसाया।