"dog used in hunting game birds," 1832, from bird (n.1) + dog (n.). Hence the verb (1941) meaning "to follow closely."
Entries linking to bird-dog
bird n.1
"feathered, warm-blooded vertebrate animal of the Aves," Old English bird, a rare collateral form of bridd, originally meaning "young bird, nestling" (the usual Old English for "bird" being fugol, for which see fowl (n.)), which is of uncertain origin with no cognates in any other Germanic language. The suggestion that it is related by umlaut to brood and breed is rejected by OED as "quite inadmissible." The metathesis of -r- and -i- was complete 15c. (compare wright).
Despite its early attestation, bridd is not necessarily the oldest form of bird. It is usually assumed that -ir- from -ri- arose by metathesis, but here, too, the Middle English form may go back to an ancient period. [Liberman]
Up to c. 1400 it still often was used in the specific sense "the young of a bird, fledgling, nestling, chick," and of the young of other animals (bees, fish, snakes) and human children. Compare the usual Balto-Slavic words for "bird" (Lithuanian paukštis, Old Church Slavonic pŭtica, Polish ptak, Russian ptica, etc.), said to be ultimately from the same root as Latin pullus "young of an animal."
The proper designation of the feathered creation is in E. fowl, which in course of time was specially applied to the gallinaceous tribe as the most important kind of bird for domestic use, and it was perhaps this appropriation of the word which led to the adoption of the name of the young animal as the general designation of the race. [Hensleigh Wedgwood, "A Dictionary of English Etymology," 1859]
The figurative sense of "secret source of information" is from 1540s. The colloquial meaning "man, fellow, person" is from 1799.
Bird-watching is attested from 1897. Bird's-eye view "the view as seen from above, as if by a bird in flight," is from 1762. Phrase for the birds in reference to anything undesirable is recorded from 1944, supposedly in allusion to birds eating from droppings of horses and cattle. The bird-spider (1800) of the American tropics is a large sort of tarantula that can capture and kill small birds.
A byrde yn honde ys better than three yn the wode. [c. 1530]
The form with bush is attested by 1630s.
dog n.
"quadruped of the genus Canis," Old English docga, a late, rare word, used in at least one Middle English source in reference specifically to a powerful breed of canine; other early Middle English uses tend to be depreciatory or abusive. Its origin remains one of the great mysteries of English etymology.
The word forced out Old English hund (the general Germanic and Indo-European word, from root from PIE root *kwon-) by 16c. and subsequently was picked up in many continental languages (French dogue (16c.), Danish dogge, German Dogge (16c.). The common Spanish word for "dog," perro, also is a mystery word of unknown origin, perhaps from Iberian. A group of Slavic "dog" words (Old Church Slavonic pisu, Polish pies, Serbo-Croatian pas) likewise is of unknown origin.
In reference to persons, by c. 1200 in abuse or contempt as "a mean, worthless fellow, currish, sneaking scoundrel." Playfully abusive sense of "rakish man," especially if young, "a sport, a gallant" is from 1610s. Slang meaning "ugly woman" is from 1930s; that of "sexually aggressive man" is from 1950s.
Many expressions — a dog's life (c. 1600), go to the dogs (1610s), dog-cheap (1520s), etc. — reflect the earlier hard use of the animals as hunting accessories, not pets. In ancient times, "the dog" was the worst throw in dice (attested in Greek, Latin, and Sanskrit, where the word for "the lucky player" was literally "the dog-killer"), which plausibly explains the Greek word for "danger," kindynos, which appears to be "play the dog" (but Beekes is against this).
Notwithstanding, as a dog hath a day, so may I perchance have time to declare it in deeds. [Princess Elizabeth, 1550]
Meaning "something poor or mediocre, a failure" is by 1936 in U.S. slang. From late 14c. as the name for a heavy metal clamp of some kind. Dog's age "a long time" is by 1836. Adjectival phrase dog-eat-dog "ruthlessly competitive" is by 1850s. Phrase put on the dog "get dressed up" (1934) may be from comparison of dog collars to the stiff stand-up shirt collars that in the 1890s were the height of male fashion (and were known as dog-collars from at least 1883).