Some suggest it has Scandinavian origins, a distant relative got a Family Name History A4 size document for the name Glasby from a company dealing in these items and it suggests the name comes from the old Scandinavian name Glathr – and the –by ending means farmstead. Meaning “dweller at farmstead or village of man named Glathr”.
I am not an expert in the surname meaning field but I have doubts about using these documents and their information as serious tools of research as they do not quote the sources used.
I have searched many a book on meanings of surnames and not found Glasby in it, though once whilst at the Nottingham Archives Office I saw a reference to a similar name – Gilasbey – see Gillespey – o “bishops servant” scots gaelic. Source: The Penguin Dictionary of Surnames. I find this rather interesting as I have not found any Scottish references to the name in the IGI, etc under the spelling Glasby. I have in the past been contacted by people researching Gillespie and a possible suggestion Glasby is a variation of this name.
There are a few variations Glasbey and Glassby the obvious ones but others I have been asked about are Glosby, Glaspie, etc.