(Variations: ass or balls or eyebrows or nuts or pajamas or whiskers may replace meow; the phrase may be shortened to the cat's) Something or someone that is superlative: The cat's pajamas!—anything that is very good/ that you are on top of things and that you are, therefore, the cat's ass
[1920+; the entry form and pajamas form are said to have been coined by the cartoonist and sports writer Tad Dorgan, who died in 1929]