1550s, a shortened form of goodwife, a term of civility applied to a married woman in humble life; hence Goody Two-shoes, name of the heroine in 1760s children's story ("The History of little Goody Two Shoes; otherwise called Mrs. Margery Two Shoes") who exulted upon acquiring a second shoe.

also goodie, "something tasty," 1745, from good (adj.) + -y (2). Adjectival use for "sentimentally proper" is by 1830 (especially in reduplicated form goody-goody, 1865). As an exclamation of pleasure, by 1796.