In Latin, audire means “to hear,” so it makes sense, then, that inaudible means “imperceptible by the ear,” since in- means “not.” You should strive to speak in a near-inaudible whisper if you need to talk to your seatmate at the opera, but in normal, everyday conversation, you won’t get your point across unless you talk at a louder volume. Synonyms for inaudible range from faint and muffled to uncommunicative and voiceless.