Smackeroo is originally (and still usually) an American slang term with three meanings: "something very good or excellent; cash, folding money; a sharp slap or hard blow (accidental or deliberate).” The etymology of smackeroo isn’t very clear: it may come from smacker “a dollar; a loud kiss,” or from the verb smack “to strike sharply; kiss loudly.” The suffix -eroo is an Americanism of uncertain origin, used for forming jocular, gaudy variants of neutral or colorless nouns, e.g., switcheroo for switch. Smackeroo entered English in the mid-20th century.
