This is about domestic cat history. The title is a Google search term but misleading because it implies that there is a creature called ‘Grimalkin Cat’. There is not. Grimalkin is a 17th century word meaning ‘a cat’, especially an old female cat.
The word grimalkin also refers to ‘a jealous of imperious old woman’.
The earliest usage of the word is found in Shakespeare’s Macbeth (1605) in which one of the three witches cries out ‘I come, Grimalkin’. It gives the impression that the witch is calling to her familiar, a domestic cat embodying the devil.
Apparently this lead to a definition of Grimalkin as ‘a fiend supposed to resemble a grey cat’.
Derivation of Grimalkin
The derivation (origin and evolution) of Grimalkin is convoluted per the book Cat World A Feline Encyclopaedia:
Grimalkin = Grey + Malkin. Malkin = Maud + kin. Maud = abbreviation of Matilda. Matilda = slang term for a slut. The word Grimalkin therefore means ‘grey-slut-kin’.
This may be connected to witches familiars. According to Brian Vesey-Fitzgerald (a naturalist and writer of books on wildlife, cats, and dogs):
“The true cat of witchcraft, the true familiar of the witch, was the grey cat, Grimalkin.”
He rejects the usual view that blacks cats were considered evil during the era when witches were burnt. He writes that old ladies during that era were not burnt at the stake because they lived with black cats. It was enough that they lived with cats.
However, Dr Morris writes that illustrations from that era almost always show black cats with witches. It is difficult therefore to accept the views of Vessey-Fitzgerald on this point. Morris leaves open the possibility that grey (gray) cats played a role in the medieval era as the embodiment of wickedness.