The word copycat is so ubiquitous, it's easy to miss when considering the origin of pet-related words or phrases.
But it's really fairly young, as words go.
It's a slang term - an Americanism. As such, it was probably in use colloquially for a bit before it first appeared in print.
It means to imitate or mimic someone or something. And it has a slightly negative or disapproving connotation. Being called a copycat isn't really a compliment, after all.
Its first use in print has been traced to a late 19th century American writer by the name of Constance Cary Harrison (we'd never heard of her, either!).
And - you'll love this! - the book was written from the point of view of a fox terrier named Dame Trot. Her canine companion was a fox terrier named Paul Pry. The book details several adventures with her human family (the master, the mistress and "our boys") in day trips set around Bar Harbor, Maine.
Here's a little snippet from the book - and incidentally, the first known use of copycat in print:
An intrepid intern at the web-based magazine, Slate, is to be commended for her sleuthing. She was the one who actually tracked this down, and the folks over at the Stack Exchange forwarded her research to the Online Etymology Dictionary for updating.
In the course of researching this, we came across a pretty nifty tool we had not known about. This tool is called the Ngram, and it tracks a word's use in print back through the centuries!
We plugged the word copycat (and all variations we could think of) into Ngram and here's what we found:
Sure enough - there's our little blip, right at 1887!
Who is copying whom, we ask?
Archive.org's online copy of Bar Harbor Days, by Constance Cary Harrison
The Stack Exchange: English Language & Usage
Google Books' Ngram site
Wikipedia on Copycat
Wikipedia on Constance Cary harrison