sweetheart; a term of endearment
trivial term of endearment, 1919, from Snooks, proper name used in Britain for "a hypothetical person" (1860), cf. Joe Blow in U.S. As an actual proper name, Snooks dates back to the Domesday Book and may be from Old English *snoc "a projecting point of land" (perhaps here with sense of "a big nose").
Precious one; sweet and dear one • Used to address small dogs, babies, etc: Yes, you are. You're my little snookums (1919+)