INAUDIBLE
inaudible, unhearable
(adjective) impossible to hear; imperceptible by the ear; “an inaudible conversation”
Source: WordNet® 3.1
Etymology
Adjective
inaudible (not comparable)
Unable to be heard or not loud enough to be heard.
Synonyms: quiet, silent, soundless, voiceless
Antonyms: audible, loud, vocal
Source: Wiktionary
In*au"di*ble, a. Etym: [L. inaudibilis; pref. in- not + audire to
hear: cf. F. unaudible. See In- not, and Audible.]
Definition: Not audible; incapable of being heard; silent.
– In*au"di*ble*ness, n.
– In*au"di*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition