Old English hund "dog," from Proto-Germanic *hundaz (source also of Old Saxon and Old Frisian hund, Old High German hunt, German Hund, Old Norse hundr, Gothic hunds), from PIE *kwnto-, dental enlargement of root *kwon- "dog." Meaning narrowed 12c. to "dog used for hunting" (compare dog (n.)). Contemptuously, of a man, from late Old English.
"hunt with hounds," 1520s, from hound (n.). Figurative sense "pursue relentlessly" first recorded c. 1600. Related: Hounded; hounding.