Of disputed origin. It has been in use since the 17th century. It is now generally taken as a feminine equivalent of Andreas, and this probably represents its actual origin. However, it was not in use in the Middle Ages, and the suggestion has also been made that it represents a coinage in English from the Greek vocabulary word andreia ‘manliness, virility’.
Scottish and northern Irish: from Anglo-Norman French waleis ‘Welsh’ (from a Germanic cognate of Old English wealh ‘foreign’), hence an ethnic name for a Welsh speaker. In some cases this clearly denoted an incomer to Scotland from Wales or the Welsh Marches, but it may also have denoted a Welsh-speaking Scot: in western Scotland around Glasgow, the Welsh-speaking Strathclyde Britons survived well into the Middle Ages.