Scottish and English.

A posting on an Ancestry Message Board [LB] notes that Ket, also known as Ketty, occurs five or six times in the 1851 Census of Fearn parish, Ross and Cromarty, Scotland. A correspondent [MG] has records of it being used as an alternative spelling for Ceit, the Scottish Gaelic variant of Kate.

Another correspondent [JB] notes the use of Kett in several generations in a family living in Dores, Inverness-shire, Scotland. The birth name, where known, was Catherine. Ket and Kett are therefore clearly variants of Kit or Kate.

Yet another correspondent [EC] reports that Ket was used as a male pet name for Christopher in parts of England in Victorian times and later. Because there is no relationship between Catherine and Christopher we do not consider the male and female versions of Ket to be associated with one another.