In a word: sockdolager

A notable contribution to the language is the nineteenth-century American colloquialism sockdolager (pronounced sahk-DAHL-uh-jer). It means, literally, "knockout punch" or "a decisive blow," figuratively something that settles a matter, the decisive thing. It also came to mean something outstanding or exceptional.

The etymology is obscure. Some speculate that it is a fanciful combination of sock, "punch" or "blow," and Doxology. In American Protestant churches the Doxology ("Praise God from whom all blessings flow") is typically sung, with vigor, as the day's offering is carried forward. (Not so in liturgically sensitive Episcopal churches, where the Doxology would provide a false climax before the Eucharistic prayer.)

Example: One of the most famous nineteenth-century occurrences of the word is a line Asa Trenchard speaks to Mrs. Mountchessington in Tom Taylor's Our American Cousin: "Well, I guess I know enough to turn you inside out, old gal, you sockdologizing old man-trap." John Wilkes Booth used the laughter at this line for cover as he fired a bullet into Abraham Lincoln's brain. They are the last words Lincoln heard in this life.