There is no meaning beyond the idiomatic; "The cat's pyjamas" was popularized in the twenties by the fashionable set, along with a lot of other like phrases such as "The bees knees" and "the clams garters". The list goes on and on, and all but the first two have virtually disappeared from our language. The phrases were just slang of the time for "cool" (or should I say 'hep'?)

This phrase comes from the early 1800's. The English taylor, E.B. Katz made silk pajamas for royalty and the wealthy. They were said to be the finest pajamas made anywhere in the land and they soon came to be known as Kat'z pajamas.

I always check out the Word Detective for these things: Ours just wear those little fur suits. Dear Word Detective: What is the derivation of the phrase "cat's pajamas"? I think it means the hottest new craze, but I don't know where it came from or why. I've never seen a cat wearing pajamas, or anything else for that matter, although my dog does have a chenille sweater. -- Susan. A chenille sweater. For your dog. And the dog actually wears said sweater? Our dog Brownie also has a thing for clothes, but with a slight difference. She regards them as a very special kind of food. So far, by my count, she has eaten six or seven socks, assorted mittens and gloves, and at least one small scarf. I guess the poor thing must have an Orlon deficiency in her diet. "The cat's pajamas" does indeed mean "the hottest new thing" or "great, wonderful" (as in "Fred's new car is the cat's pajamas; Fred himself, not so much"). But I'm wondering where you're running into "the cat's pajamas" these days, because the phrase itself is nearing its one-hundredth anniversary. "The cat's pajamas" is first recorded in 1920 as part of the typical vocabulary of the "flappers," young women whose avant-garde wardrobe and free-spirited disregard for popular mores epitomized the spirit of the Roaring Twenties. The term "flapper" itself had appeared about 1915 (although an antecedent meaning of "young prostitute" was current in the late 19th century), and was most likely an adaptation of "flapper" in the 18th century sense of "a young duck or partridge" (i.e., one given to much flapping but inept flight). According to Stuart Berg Flexner's "Listening to America" (1982), "the cat's pajamas" was one of a number of nonsense phrases invented in the flapper period, often on the template of combining an animal, the more unlikely the better, with a part of the human body or an article of clothing. Thus "the cat's pajamas" seems to have inspired a rash of similar phrases also meaning "excellent," including "the bee's knees," "the clam's garters," "the eel's ankles," "the gnat's elbow," "the pig's wings" and my personal fave, "the sardine's whiskers." While none of these phrases or dozens of other have any intrinsic logic (don't go looking for an eel's ankle, in other words), the formula does have the advantage of nearly infinite variation, and one can easily imagine a hipster of the day poring over zoology textbooks in search of ever more exotic species with which to wow the gang. While "the cat's pajamas" doesn't really mean anything, it is worth noting that in 1920 pajamas were still a relatively new form of sleep apparel (as opposed to nightshirts and nightgowns), and thus were still considered slightly risque, especially for young women. http://www.word-detective.com/0807A.html#catspajamas

I think Jimma's got it. This sounds plausiable. The term "cat's pajamas" comes from E.B. Katz, an English tailor of the late 1700's and early 1800's, who made the finest silk pajamas for royalty and other wealth patrons. Nothing like a cat nap in Kat'z pjs. (from the book, "Cats out of the Bag" compiled by Terry, Don and Ken Beck);