English from Greek "pure". Also the French form of Katherine [q.v.] and its variants Katharine/Catharine.
The main spellings occurring in the 1841 Census of Aberdeenshire are Catharine [25%], Catherine [60%], Katharine [4%], Katherine [4%]. In the 1851 Census of the parish of Rathen, Scotland, there is a very high proportion of Catherine [70%] and Cathrine [25%] with no significant other spelling; this may reflect the preferences of the enumerators for that parish. There are many other variations in spelling. Those occurring more frequently in the 1841 Census of Aberdeenshire are shown below.
The FreeREG list of Latin names used in old documents shows Catalina as being the equivalent of Catherine and Catherina/Katherina/Katalina being the equivalent of Katherine. We are not convinced that such subtle differentiation is entirely consistent. Whatever the truth of it, care is needed when searching old documents as clearly there will be some variation in the names, even as there is today. Use truncated names [e.g. Catherin*] to avoid difficulties with Latin case endings.
Kitty has been found as an occasional pet name.
A correspondent [RB] has noted an ancestor's sister, baptised Catherine in Grange, Banffshire, Scotland, who was known to the family as Kathleen. Another correspondent [AB] has a similar occurrence in the mid 18th century. Both names are Anglicized forms of Caitlin and are classed here as lesser synonyms as there is no other connection between the names.
Note Some details, where specific, are included under Katharine, Catherine and Catharine but, as in the Oxford Names Companion, we have given the most complete set of relationships under Katherine [q.v.].