past tense and past participle of hear, Old English herde. To have heard of "know about" is from 1907.
Entries linking to heard
Old English heran (Anglian), (ge)hieran, hyran (West Saxon) "to hear, perceive by the ear, listen (to), obey, follow; accede to, grant; judge," from Proto-Germanic *hausejanan (source also of Old Norse heyra, Old Frisian hera, hora, Dutch horen, German hören, Gothic hausjan "to hear"), from PIE root *kous- "to hear" (source also of Greek koein "to mark, perceive, hear;" see acoustic). The shift from *-s- to -r- is a regular feature in some Germanic languages. For the vowels, see head (n.).
Spelling distinction between hear and here developed 1200-1550. Meaning "be told, learn by report" is from early 14c. Old English also had the excellent adjective hiersum "ready to hear, obedient," literally "hear-some" with suffix from handsome, etc. Hear, hear! (1680s) originally was imperative, an exclamation to call attention to a speaker's words ("hear him!"); now a general cheer of approval. To not hear of "have nothing to do with" is from 1754.