The term 'tomcat' is a classic example of anthropomorphism in English, where a common human name is attached to an animal to denote its gender. The name "Tom" was popularized for this purpose in the 18th century, notably through the 1760 book "The Life and Adventures of a Cat" by an anonymous author, whose protagonist was a male cat named Tom. This literary usage cemented the generic association of "Tom" with maleness in felines. The compound thus follows a simple, transparent logic: a cat that is male is a 'Tom' cat, analogous to terms like "billy goat".

This is a compound word formed from the common English given name "Tom" and the common noun "cat". "Tom" is a hypocorism (pet form) of the name "Thomas", ultimately from Aramaic, and is used here generically to personify a male. "Cat" is from Old English "catt", from Late Latin "cattus".