1520s, cubbe "young fox," of unknown origin, not recorded in Middle English; perhaps from Old Irish cuib "whelp," or from Old Norse kobbi "seal." Extended to the young of bears, lions, etc., after 1590s. The native word was whelp. Cub Scout is from 1922.
late 15c., "woman's small pet dog," a word of uncertain origin but likely to be from French poupée "doll, toy" (see puppet). "A little dog appears to have been called puppy because petted as a doll or puppet" [Century Dictionary].
The meaning shifted from "toy dog" to "young dog" (1590s), replacing native whelp. In early use in English the words puppet and puppy were not always distinguished. The word also was used from about that time in the contemptuous sense of "vain or silly young man."
Puppy-dog is attested by 1590s (in Shakespeare, puppi-dogges). Puppy love "juvenile infatuation" is from 1823. Puppy fat "excessive fat on a child or adolescent" is by 1913 (in reference to young dogs by 1894).
breed of dog, a kind of sheep-dog much esteemed in Scotland, 1650s, of uncertain origin. Possibly from dialectal coaly "coal-black," the color of some breeds (compare colley, "sheep with black face and legs," attested from 1793; Middle English colfox, "coal-fox," a variety of fox with tail and both ears tipped with black; and colley, Somerset dialectal name for "blackbird"). Or from Scandinavian proper name Colle, which is known to have been applied to dogs in Middle English ("Ran Colle our dogge, and Talbot, and Gerlond" [Chaucer, "Nun's Priest's Tale"]). Century Dictionary cites Gaelic cuilean, cuilein "a whelp, puppy, cub." Or perhaps it is a convergence of them. Border-collie (by 1894) was so called from being bred in the border region between Scotland and England.