Older Slang.
1. something unusually large, heavy, etc.
2. a decisive reply, argument, etc.
3. a heavy, finishing blow: His right jab is a real sockdolager.

Sockdologising was nearly the last word President Abraham Lincoln heard. On April 14, 1865, assassin John Wilkes Booth stepped closer to President Lincoln, gun in hand while everyone else watched “Our American Cousin.” Booth knew the play well and waited for the line, “Well, I guess I know enough to turn you inside out, you sockdologising old man-trap.” As the audience laughed, Booth aimed and fired at point-blank range, mortally wounding the President.

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