Stories We Like: A Guide to the Comma
late 15c., "woman's small pet dog," of uncertain origin but likely from Middle French poupée "doll, toy" (see puppet). Meaning shifted from "toy dog" to "young dog" (1590s), replacing Middle English whelp. In early use in English puppet and puppy were not always distinct from each other. Also used about that time in sense of "vain young man." Puppy-dog first attested 1590s (in Shakespeare, puppi-dogges). Puppy love is from 1823. Puppy fat is from 1937.