What's the origin of "Copycat"?

Solution 1:

The cat in copy-cat means person.

The OED says at copy-cat n.:

Etymology: cat n.¹ 2.

the referenced sense being:

cat n.¹ 2. fig. a. As a term of contempt for a human being; esp. one who scratches like a cat; a spiteful or backbiting woman. spec. an itinerant worker (U.S. slang).

Solution 2:

This is a slang term and was likely used in speech for a long time before being committed to the page, but the first print copy can still give us a rough idea of origin. Etymonline.com tells us:

copycat (n.)
by 1884, Amer.Eng., probably at least a generation older, from copy + cat. As a verb, from 1932.

This Ngram tends to agree, with some instances before 1900, fairly constant use for most of the 20th century, but then a huge increase in the 1980s.

The OED's earliest citation is Jewett's 1896, so I've sent them the Harrison 1887 and Jewett 1890 antedatings from the Slate article.

An article in Slate Magazine tells us the term came from nineteenth-century Maine.

Constance Cary Harrison's 1887 quasi-memoir Bar Harbor Days contains the first written evidence of the term copycat—that we know of, anyway. "Our boys say you are a copy cat, if you write in anything that's been already printed." Another early example comes from a different Maine-born writer, Sarah Orne Jewett, in her 1890 novel Betty Leicester: A Story for Girls. "I wouldn't be such a copy-cat," Lizzie French tells Betty, upon hearing that Betty wants to start a second all-girls club. Jewett used it again in her 1896 novel Country of Pointed Firs, about an elderly landlady in small-town coastal Maine who tells her friend Mrs. Fosdick, "In these days, the young folk is all copy-cats, 'fraid to death they won't be all just alike." Mrs. Fosdick's response suggests that the term had been part of the spoken vernacular for some time: "I ain't heard of a copy-cat this great many years," said Mrs. Fosdick, laughing; " 'twas a favorite term o' my grandmother's."

The OED's earliest citation is Jewett's 1896, so I've sent them the Harrison 1887 and Jewett 1890 antedatings from Slate Magazine.

Solution 3:

1. Not good to call a friend a copycat, and if you do, etymology is your least concern
2. See this Slate article regarding why it's not "copymonkey", etc., especially regarding the time of the origin of "hell-cat"
3. The origin of the term is unknown and likely unknowable at this point