Liam is a short form of the Irish name, "Uilliam", itself a derivative of the Frankish, "Willahelm". The original name was a merging of the Old German elements, vila ("will" or "resolution") and helma ("helmet"), and therefore, means "helmet of will". When the Frankish Empire was divided into two parts, the name developed differently in each region. In the French half, Willahelm developed first into "Guilielm", and then into "Guillaume".
Read more about Liam: Origin, 21st Century, People