An etymological orphan of unknown origin that somehow overthrew the ancient word 'hound' to become universal.
A domesticated carnivorous mammal (Canis familiaris) kept as a pet, for hunting, herding, or other work. The most widely kept companion animal in human history.
The word 'dog' is one of the great mysteries of English etymology. It appears in late Old English as 'docga,' initially referring to a specific powerful breed, while the standard Old English word for the animal was 'hund' (cognate with German 'Hund' and Latin 'canis'). No one has convincingly explained where 'docga' came from — it has no known cognates in any other Germanic language
English 'dog' replaced the original word 'hound' so completely that 'hound' narrowed to mean only a hunting dog — yet no one knows where the word 'dog' actually came from, making it one of the most successful etymological orphans in any language.