Unheard

wiktionary

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un- +‎  heard

See the etymology of the corresponding lemma form.

etymonline

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unheard (adj.)

c. 1300 "not detected by sense of hearing," from un- (1) "not" + past participle of hear. Meaning "unknown, new" is attested from late 14c. (Old English had ungehered in this sense). Usually with of since 1590s. Similar formation in Old Norse oheyrðr, Danish uhørt, Middle Dutch ongehoort, Old High German ungehoret.