Liam is a short form of the Germanic name William, or its Irish variant Uilliam. Etymology. The original name was a merging of two Old German elements: willa ("will" or "resolution"); and helma ("helmet"). The juxtaposition of these elements effectively means "helmet of will" or "guardian". When the Frankish Empire was divided, the name developed differently in each region. In Northern Francia, Willahelm developed first into "Willelm" and then into "Willaume" in Norman and Picard, and "Guillaume" in Ile-de-France French.
https://en.wikipedia.org/wiki/Liam