Latinate name, first used by Shakespeare for the rich heiress wooed by the duke in Twelfth Night (1599). Shakespeare may have taken it as a feminine form of Oliver or he may have derived it from Latin oliva ‘olive’. In the 1970s it was particularly associated with the Australian pop singer and actress Olivia Newton-John (b. 1948). Since the 1990s it has been very popular throughout the English-speaking world.
English: patronymic from Weather, from Middle English wether ‘wether’, ‘(castrated) ram’ (Old English weðer), hence a nickname for a man supposedly resembling a wether, or a metonymic occupational name for a shepherd.